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Tue UNIVERSITY OF CHICAGO PUBLICATIONS 
IN RELIGIoUS EDUCATION 
EDITED BY 


ERNEST D. BURTON SHAILER MATHEWS 
THEODORE G. SOARES 


CONSTRUCTIVE STUDIES 



















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Nettie li ii en NO hOUR TEL 
GENERATION 


THE UNIVERSITY OF CHICAGO PRESS 
CHICAGO, ILLINOIS 


THE BAKER & TAYLOR COMPANY 
NEW YORK 


THE J. K. GILL COMPANY 
PORTLAND, OREGON 


THE CUNNINGHAM, CURTISS & WELCH COMPANY 
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THE CAMBRIDGE UNIVERSITY PRESS 
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Digitized by the Internet Archive 
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NVIHO ‘NOIdNVHO DNILLOWL LNaSdadd AHL 


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Wish 
THIRD avd FOURTH 
GENERATION 


AN INTRODUCTION TO HEREDITY 


By 
ELLior RowLAnpD DowNnING 


The School of Education NE PRINAE 
University of Chicago r Oi NCETp 





NS 
A ectals 
Ly Le. ** 


me 


THE UNIVERSITY OF CHICAGO PRESS 
CHICAGO, ILLINOIS 





COPYRIGHT 1918 By 
THE UNIVERSITY OF CHICAGO 


All Rights Reserved 


Published January 1918 


Composed and Printed By 
The University of Chicago Press 
Chicago, Illinois, U.S.A. 


EDITORS’ PREFACE 


The curriculum of the church school of 
religious education is rapidly widening. This 
does not mean that the study of the Bible is 
decreasing, but that more time is devoted to 
the study of the religious significance of life. 
A variety of important subjects dealing with 
social and ethical problems is occupying the 
attention of young men’s and young women’s 
classes and of young people’s clubs and socie- 
ties. Bible study becomes more significant 
as it takes its place among all the human 
interests. 

The public school is recognizing its respon- 
sibility for larger social education and, wherever 
young people are receiving adequate instruction 
in the duties of modern life the task of the 
church is so far lightened. But there are many 
social studies which are peculiarly well under- 
taken in the religious atmosphere; and there 
is a very large body of young people in the 


vii 


Vill EDITORS’ PREFACE 


churches who have never completed a high- 
school education and for whom the church has 
important educational responsibility. There- 
fore, without in any wise undertaking to parallel 
the work of the high school, the curriculum of 
religious education may well include a wide 
range of social studies. 

For these reasons the scheme of the Con- 
structive Studies has contemplated very much 
more than the biblical elements. Beginning 
with Henderson’s Social Duties from the Chris- 
tian Point of View a series of textbooks deal- 
ing with important social problems has been 
gradually developed. 

The present study is an attempt to consider 
frankly and seriously the scientific facts regard- 
ing the problem commonly called “eugenics.” 
The religious significance of a reverent and 
thoughtful understanding of this highly interest- 
ing subject is at once apparent when one thinks 
of the perfecting of human society as the goal 
of the divine plan. The scientist, as such, will 
not of course discuss the spiritual significance 
of the evolutionary goal. That is where faith 


EDITORS’ PREFACE ix 


goes beyond our ascertained knowledge. But 
faith must not operate apart from knowledge. 
Nothing can be more important in religious 
education than to train young people to use 
the careful methods of science in ascertaining 
the facts upon which their conclusions, not less 
in morals and religion than in other fields, are 
always to be based. The author of this volume 
is a most successful teacher, and he has suc- 
ceeded in presenting the technical aspects of 
the subject in a simple and popular way. 

While the book has been prepared for young 
people’s classes, the editors would commend 
it to the reading of ministers and laymen who 
are desirous of obtaining in untechnical lan- 
guage the results which scholars have arrived 
at in this modern attack upon the problem of 
evolution. 


5 As, aati S 





CONTENTS 


CHAPTER PAGE 


Eee PRODUCTION? ("ett es bee tp tet fF nk ete I 


Il. Some FAMousS RACERS AND THE PROBLEMS THEY 


eS rie (2 one) enh ead tae) Zit wh oa 4 
LEEPENTA CESAND iE DACA TI cut Meath ec) (oa kv meal, FO 
LV OOME LAWS ORMEREDITY rag ote. We eo 30 

West ANGARCORICA TORN te sami lS Ae eh OAD 
Nice He WAStBEL: DAStS OF TEREDITY.| if rony. 0: = 06 
Vile SOME APPARENT EXCEPTIONS: 202 0... 405 (te © 86 


VIII. ARE ACQUIRED MODIFICATIONS HERITABLE? . IOI 


IX. THE INHERITANCE OF HUMAN CHARACTERS, 
PAMSICATSANDOMLENTAL 4 bc Gooch oy oe eet Dee 


X. THE PRACTICAL PROBLEM OF HUMAN HEREDITY 147 


APPENDIX: BOOKS FOR REFERENCE OR FURTHER 
READING tes ht ean) ein yan a ecient ESO 


Ree Mee sie ey Mourn ete” | Demy i. ac) tet ate 42 59 





CHAPTER I 
INTRODUCTION 


Scientists have accumulated more accurate 
information regarding the laws and the physical 
basis of heredity in the last fifty years than the 
world acquired in the preceding fifty centuries. 
Indeed the most important part of this knowl- 
edge has come to light within two decades. 
Moreover it is knowledge of immense practical 
value, the sort that will certainly affect human 
life and racial destiny. ‘This does not imply 
that all the problems of heredity are settled or 
that our knowledge of its laws is complete: 
far from it. No one realizes as well as the 
student of these phenomena how fragmentary 
and incomplete is our present knowledge, but 
enough has been achieved to afford some 
rational foundation for human action. It is 
generally recognized that important discoveries 
have recently been made along these lines, but 
the prevailing ideas regarding these and their 


I 


2 Toe THIRD AND FoURTH GENERATION 


import are hazy and misleading. It seems wise 
therefore to present the new data simply that 
as common knowledge they may become a basis 
of wise individual conduct and may help mold 
public opinion on some important social ques- 
ions er 

This book is intended primarily for young 
people. They can most readily break away 
from the whims and prejudices of the past and 
adopt a new set of ideas as adequate grounds for 
new habits. They live only in this scientific 
age when we have an increasing respect for facts, 
reason on them to correct conclusions, and base 
on them our sense of duty. They are practical 
optimists, and what seems an impossible dream 
of the visionary to an older generation, hide- 
bound by preconceived notions and_ social 
traditions, comes to be, for valorous youth, a 
simple accomplishment dictated by good sense. 

It has been the aim to make the presentation 
as simple and non-technical as possible. So 
many of the concepts dealt with are rather new 
to the average reader that some of the chapters 
at least will need study rather than mere read- 


INTRODUCTION. 2 


ing. The book used in classes or reading circles 
does not presuppose a teacher who is already 
familiar with the subject-matter, merely one 
who.is willing to re-read and think until the | 
matter becomes reasonably clear. It is sug- 
gested that after reading each chapter individu- 
ally the group should come together to discuss 
the content. The appended list of books will 
be an aid to those who wish to read more widely 
on the topics presented or who wish to prepare 
reports for the class on particularly interesting 
phases of the subject. 


CHAPTER @IE 


~ SOME FAMOUS RACERS AND THE PROBLEMS 
THEY SUGGEST 

Every red-blooded individual is frankly 
interested in horse races, stock shows, boxing 
bouts, billiard matches, tennis tournaments, 
battles, and wars. The race has spent so much 
of its history in the struggle to get on that 
anything which pertains to physical fitness 
and mental alertness stirs deep-seated fibers of 
our being. A fine specimen of a horse, a 
blooded milch cow with a record for butter-fat 
production, a champion tennis player who has 
successfully pitted wit and skill against keen 
rivals, a victorious army, all make insistent 
appeal and receive our admiration, even our 
homage. We recognize that back of the win- 
ning performance there is a record of racial 
improvement and individual development which 
required the exercise of many admirable traits. 

In seventy years the record for the trotted 
mile has been reduced from 2:245 to 1:54-, an 


4 


RACERS AND PROBLEMS THEY SUGGEST 5 


improvement of nearly 30 per cent. There is 
given in Table I the list of American horses that 
have successively lowered the record. 











TABLE I 
Wiles LEI pie sie fea be cet 1845-59 | 2:24} to 2:192 
WP ie gis AA yk Rage Nae DI 1867 yo i TS 
SRSRISTITIA Te VLAICL sk toe, cha noes ont 1872 22162 
MD CAUENE re uch. oe vieligee os cn s 1873 22162 
PSORdSnsit ie Waite oe ook, vis 3 1874 2:14 
POAT aNyaras Wty Menta tus, La Bak Ss 1878 2a 
ue MULICN vine ns aes ee ost a ose en 1879 2:122 
AE fe OSG ca le Sr oe AR ea te ae 1880 2:112 
Sey MLL een Methinks «5G 1880 - 2:11} 
IY LETRAS homo Peat bb OMNIS eh gee ees 1880 2: 10% 
BERG) yee Mckee, vista cde, ol eae 1881 2:10; 
FOV ALS Y CES CR dl vas ae trates fod Gio uss 1884 ZITO 
Mauda trac aie 3G Stee BI On 1884 2:00% 
VLA Ch Sa ates ak es oars bats 1885 2:082 
BULL ete eats, adie sie Pew. e He as 1886 2:08% 
PARC VELI ANS cre eae taeda ca Oy 1892 2:04 
Fe Als EASES Gat ee Le 1893 2:03% 
Bar WG TAK DOL alot ethen a ikea ora 04s 1900 23037 
RCMCCUM IS perteuar aL Wee ee iicheke s IQOL 23027 
iMere iP BY LA Taye Saket Mo GaN 2 Wi aa Aint 1903 2:00 
AE TOROS ie whthides Nts st ooh ao, 1903 12502 
EUAIUUAON oii er eo Rida rune ey 1905 12583 
LIRIAS peer eters sue Ne ache a ale: 1913 7764 





*Without windshield or running pace setter 1:58. 


What are the factors which, since the days 
of Flora Temple, have brought about the 
marked improvement that enables the present 
champion to do the mile in less than two 
minutes? Some of them are very evident. 


6 Tue Turrp AND FourtH GENERATION 


More than four seconds was clipped from the 
record when, in 1892, the bicycle sulky replaced 
the old wooden affair. Some of the increased 
speed is undoubtedly due to the improvement 
in the race track and in methods of training. 
But these are not all, and probably not the most 
important factors, else a skilful trainer should 
be able to harness any horse to a modern sulky 
and get racing speed out of him. 

Racing speed seems to be in the blood. 
Look up the ancestry of this list of record- 
breaking racers and you will be struck at once 
by the recurrence, time after time, of a few 
famous breeding animals in the pedigree of 
nearly all of them. Notice the ancestry 
of Alix, a horse chosen because it is possible to 
trace his pedigree much more completely from 
available sources than that of most of the 
others. Even so, only 2090 of his ancestors 
have been found out of a possible 1,022 back 
to the ninth generation (2 parents+4 grand- 
parents+8 great-grandparents+16+32+64+ 
128+256+512=1,022). Out of these known 
290 Imported Messenger occurs 33 times, his 

















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RACERS AND PROBLEMS THEY SUGGEST 7 


parents or grandparents 64 times. Or, to put 
the matter in another way, out of 96 known 
animals in the ninth generation of Alix’ pedi- 
gree, Messenger, his parents and grandparents 
make up 65. If the same holds true for the 
unknown lines of ancestry, Alix is at least 60 
per cent Messenger blood. 

Imported Messenger was an English stallion 
brought into this country in 1788; he traces 
back to Godolphin Arabian and Darley Arabian, 
from which stock England’s best racers are 
derived. Many of the other animals in this 
ninth generation of Alix’ ancestry, such as 
Diomed, Fireaway, and Highflyer, also come 
' from these same Arabians. 

If the male line is traced in all recorded 
American trotters, going back of the sire to the 
grandsire, to the great-grandsire, and so on, it 
is found that out of 22,238 animals registered | 
to the end of 1906, 16,495 descended ‘‘in tail- 
male”’—as this particular line of descent is 
designated—from Imported Messenger; 170 
out of the 180 trotters of the 2:10 class are also 
so derived from him, and 146 out of 150 of the 


8 THE THIRD AND FOURTH GENERATION 


most famous pacers are taken from him “in the 
tail-male line.” 7 
It seems very evident from the study of such 
pedigrees that ability to produce exceptional 
speed on the track runs in families and that 
pride in ancestry is perfectly justifiable among 
race horses. The same thing is apparent if 
we consider any other animal ability, such as 
milk production in cows, pointing in dogs, or 
honey production in bees. Thus in the case 
of King Melia Rioter 14, a famous Jersey bull, 
sire of splendidly productive milkers, the same 
animals have so often reappeared repeatedly 
in the ancestry of both sire and dam, as is seen 
in the partial pedigree below, that he is more 
than go per cent (93.85) inbred. If an animal 
were derived from the offspring of a mating of 
brother and sister, he would be considered 100 
per cent inbred. ; 
The breeder appears to be trying, either by 
skill or luck, to sort and recombine the elements 
that enter into successful animals and that 
make for efficiency, taking this trait from one 
strain, that from another, and uniting them 


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RACERS AND PROBLEMS THEY SUGGEST 


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10060U§s THe: THIRD AND FOURTH GENERATION 


in anew combination with the hope of producing 
a.still better type. 

There seems to be abundant evidence that 
ability similarly runs in human families. Here 
is given the chart of family connections in the 
Darwin-Wedgewood-Galton family (see Plate I). 
This tabulation traces the lines back to Josiah 
Wedgewood, founder of the famous potteries, 
to Erasmus Darwin, philosopher and author, 
and to Samuel Galton. All three were men of 
marked distinction, the first two members of 
the Royal Society. Men of marked ability are 
indicated in the chart by black squares; those 
who, in addition, are members of the Royal 
Society are shown with an R beside the square. 
There is unfortunately no criterion for judging 
the degree of distinction of the women (repre- 
sented by circles) as exists in biographical dic- 
tionaries or membership in learned societies for 
men. Charles Darwin, one of the most noted 
of biologists, himself a member of the Royal 
Society, comes from a father who was a mem- 
ber and from grandfathers both of whom were 


also members of the same distinguished organi- 


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RACERS AND PROBLEMS THEY SUGGEST II 


zation. His wife comes from equally able 
parentage. ‘Three of their sons were also mem- 
bers of the Royal Society, one of the Royal 
Geographic Society; two of their grandsons are 
already men of marked ability. 

The son of an able man is much more likely 
to display ability than the average person. 
Sir Francis Galton, in the above-mentioned 
family, devoted his life to studies of human 
heredity. In his book on Heredity Genius he 
gives some of the important results of his 
studies. He looked up the family connections 
of all the great English judges who lived in the 
period from 1660-1865. ‘There were 268 of 
them of sufficient distinction to be included 
in Foss’s Lives of the Judges; tog of these had 
one or more eminent relatives. Close relatives 
were more likely to be eminent than distant 
relatives. C. W. Saleeby in his Parenthood and 
Race Culture reduces Galton’s results to the 
following statement: sons of judges have 126 
chances out of 1,000 of achieving greatness, 
brothers 82, grandsons 37, and nephews 17. 
To give these figures any significance we must 


12 THE THIRD AND FouRTH GENERATION 


know what the chance is for the average man. 
Galton calculated this, too. He assumed that 
a man would display marked ability by fifty 
years of age if he was ever going to do so. So 
by comparing the number of men in the English 
Men of the Time, later known as Who’s Who, 
with the total number of Englishmen of fifty 
or more he found the chance of the average 
man to achieve distinction to be 1 to 4,000. 
So the son of a judge is 500 times as likely to 
display ability as the son of the average man, 
which Galton thinks is due in large part to his 
inheritance. Galton’s investigation included 
not only judges, but also scientists, artists, 
statesmen, and others, embracing in its scope 
nearly a thousand families. The conclusions 
reached substantiate those given for the judges. 

There is given here the family tree of the Bach 
family, of which Johann Sebastian Bach, organist 
and composer, was the most noted. The family 
sprang from well-to-do Thuringian peasant stock 
that manifested marked musical ability even 
before the records are sufficiently accurate to 
show what relation these early talented indi- 


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RACERS AND PROBLEMS THEY SUGGEST 13 


viduals were to Sebastian’s immediate ancestry. 
In six generations there appeared 57 musicians 
of repute, 29 of whom were really noted. 

The best-known illustration of inherited 
ability in American families is found in the 
descendants of Jonathan Edwards, and there is 
usually contrasted with this Edwards family of 
noted people a contemporaneous but notori- 
ous family, known as the Max-Jukes, whose 
pedigree was traced to 1874 in detail by 
R. A. Dugdale and to 1915 by Estabrook. 
Dugdale’s data were published in the 7 wentzeth 
Annual Report of the New York State Prison 
Commission, later appearing as a book from the 
press of G. P. Putnam’s Sons. The results of 
Estabrook’s investigations appear as a publica- 
tion of the Carnegie Institution, Washington, 
D.C. The contrasting records of the two fam- 


ilies are given below: 


Jonathan Edwards’ Descendants 


1,394 descendants traced in 1900 
Not a pauper among them but many professional 
men, including: 


60 physicians 


14 ‘THE THIRD AND FOURTH GENERATION 


60 or more authors 

100 Or more ministers and missionaries 
100 lawyers 

75 army officers 

295 college graduates 

13 college presidents 


Max-Jukes’s Descendants 

About 1,200 known in 1874; 2,094 to I9I5 

1,258 now living in this country 

310 paupers (Dugdale) 

Over 600 of those living are feeble-minded or 
epileptic (Estabrook) 

More than 300 immoral women (Dugdale) 

140 criminals, 7 murderers 

Not a soldier among them 

Not one had a common-school education 

Only 20 learned a trade, 10 of those in prison 

The family has cost society over $2,500,000 


Similar contrasts are undoubtedly to be found 
in many other families, but this one has been 
carefully worked out. Jonathan Edwards 
(1703-58), whom Daniel Webster called the most 
brilliant logician America has produced, came 
of Welsh stock. His great-great-grandfather 
was a prominent clergyman of London in the 


RACERS AND PROBLEMS THEY SUGGEST 15 


days of Shakespeare and Bacon. The son of 
this clergyman came to the New England 
colonies and was a prosperous merchant of 
Hartford, Connecticut, as was his only son, 
Richard. This Richard’s wife was Mary 
Tuttle, a commanding and brilliant woman. 
Their only son, Timothy, was a clergyman, a 
Harvard honor man, the father of eleven 
children, of whom the fifth was Jonathan. 
Jonathan’s mother as well as his wife were . 
from fine types of American families. 

The Max-Jukes family originated in Sullivan 
County, New York, into which isolated region, 
to quote Dugdale’s account, “now within two 
hours’ rail journey of the nation’s metropolis, 
there drifted nearly a century and a half ago 
a number of persons whose constitutions did 
not fit them for participation in a_ highly 
organized society: Max, the hunter and fisher, 
the jolly, alcoholic ne’er-do-well; Lem, the 
stealer of sheep; Lawrence, the licentious, free 
with his gun; Margaret and Delia, the wantons, 
and Belle who had three children by various 
negroes.” From this bad stock has come the 


16 THe THIRD AND FOURTH GENERATION 


strain known as the Max-Jukes, and whether 
the descendants are found in Connecticut, in 
New Jersey, or even in Minnesota, they mani- 
fest the same feeble-mindedness, indolence, 
licentiousness, and dishonesty. 

In the foregoing case as well as in the family 
history of the Darwins and the Bachs there is 
considerable inbreeding, that is, mating between 
individuals: that are closly related. Such mat- 
ings are intentionally carried out by the 
breeder in the production of fine horses and 
cattle, as seen in the pedigrees already given. 
They seem to serve to emphasize what is in the 
strain. If superior stock is used, inbreeding 
merely prevents its dilution. If poor stock is 
used, the inferior qualities continually reappear 
in the offspring. Three of the four children of 
Ada Jukes married cousins, with appalling 
results. Charles Darwin married a cousin, as 
did also his grandfather Wedgewood. Johann 
Sebastian Bach was twice married, each time 
to a Bach. The Darwin and Bach children 
manifest the same desirable qualities as the 
parents. 


RACERS AND PROBLEMS THEY SUGGEST 17 


In all such cases as that of the Jukes and 
Edwards families we cannot be sure that the 
unlike environments in which the children were 
reared may not have been in large measure 
responsible for the strikingly different character 
of the offspring. Although the families were 
contemporaries and lived in adjoining states, 
yet the home atmospheres, the real environ- 
mental influences, were diametrically opposite. 
This brings up the much-debated question as to 
which is the more potent, environment or 
heredity. Such a question is about as sane as 
whether wind or water is the more important in 
the production of the waves that surge in along 
the ocean shore. ‘The simple fact is, the destiny 
of the individual is the resultant of heredity 
(what he is), environment (what he has), and 
training (what he does), and no one element 
can be omitted in calculating the results. The 
object of this book is to show how important 
heredity is and in what ways it is important. 


QUESTIONS 


t. Consider carefully the reduction in time for the 
trotted mile since the days of Flora Temple. Estimate 


18 THe THIRD AND FOURTH GENERATION 


the influence of changes in racing paraphernalia that 
have helped to bring about the improvement. What 
facts seem to show that racing ability is in the blood? 

2. Is there evidence that ability in other anir al 
activities is similarly heritable ? 

3. Can you discover human pedigrees other than 
those cited in this chapter that illustrate the matter 
under discussion ? 

4. What seems to you to be the value of ‘the 
Wedgewood-Darwin-Galton family tree as showing that 
ability is transmitted from parent to offspring in human 
families ? 

5. Will you summarize the data Galton accu- 
mulated from the study of the families of English 
judges and state your judgment as to how far the 
child of able parents is more likely to display ability 
than the child of average parents ? 

6. What do you think is the meaning of the contrast 
in the achievements of the descendants of Jonathan 
Edwards and of Max Jukes? | 

7. What would be your conclusion from the facts 
given in the chapter ? 


Os aM eed Pod hs GE 
MALE AND FEMALE 


The phenomena of heredity, in all the higher 
plants and animals, are so closely linked with 
the process of sexual reproduction that it will 
be well to review here the simple and familiar 
phases of this process. 

Recall the parts of any familiar flower, or, 
better still, re-examine some one that is at hand, 
such as the May apple, cherry, or garden pea. 
The May apple or mandrake flower is a large 
creamy bloom (Fig. 1) with from six to nine 
conspicuous white leaflike parts, the petals, 
that in the bud protect the more essential 
inner organs. Outside of these petals are 
three greenish sepals, also leaflike and pro- 
tective. The essential organs at the center 
of the blossom are the stamens and the pistil. 
The latter is quite large, is green and shaped 
like a tenpin or Indian club, with a very 
short neck. The stamens each consist of a 


TQ 


20 THe THIRD AND FOURTH GENERATION 


stalk or filament that bears at its upper end a 
yellow case, the anther. Similar parts will be 
found with varying number and arrangement 





Fic. 1.—The mandrake blossom 


in almost any flower. They are shown in the 
figure here. 

If the swollen basal part of the pistil is cut 
open, it will be seen to contain, in either the 
mandrake or the garden pea, a number of small 
bodies which you are inclined to call the seeds. 


MALE AND FEMALE 21 


They are not such as yet, however, though they 
may later develop into seeds. They are called 
ovules, and in each one, in the newly opened 
flower, there is to be found an egg, a speck of 
living substance which may later produce the 
little plant within the seed. The egg is so 
small that it is seen only with the aid of a 
microscope. ‘The swollen base of the pistil 
is known as the ovary, the name given to the 
part in plant or animal in which the eggs are 
formed. , | 

When the term “egg’’ is used the average 
person thinks first of a hen’s egg or possibly of 
some other bird’s egg as the best known type. 
But a hen’s egg is really much more than a 
simple egg; it is also a great mass of nutritive 
material inclosed in a shell to nourish and 
protect the little chick. If a hen’s egg is laid 
on the table and allowed to stand for a few 
minutes, and the shell is then cut open with a 
pair of fine-pointed scissors and the portion of 
the shell above the yolk is removed, there will 
~ be seen floating on the yolk a little fleck of 
translucent substance, like a bit of jelly (Fig. 2). 


22 Tue THIRD AND FOURTH GENERATION 


It is from this tiny speck of living substance 
that the chick develops, and this is quite com- 
parable to the egg that the plant ovule contains. 

But neither the hen’s egg nor the plant egg 
will develop into the new individual—plant or 
chick—unless it is fertilized. The anthers on 





Fic. 2.—The hen’s egg opened 


the stamens contain a yellow powder, the pol- 
len, the grains of which are often wonderfully 
beautiful. Each grain is really a living cell 
made of the same sort of substance that also 
constitutes the egg. You will recall this yellow 
dust in the case of the Easter lily, in which it is 
very conspicuous; and probably as a child you 
have stuck your nose into some flower on 
purpose to get it dusted with the yellow pollen. 


MALE AND FEMALE 23 


Some of the pollen is carried by the wind or by 
insects to the sticky or hairy upper end of the 
pistil, called the stigma. ‘The pollen grains each 
thrust out a tiny thread of their living substance, 
finer than a hair, that grows 
down through the tissue of 
the pistil until it reaches an 
ovule (Fig. 3). The thread 
penetrates the ovule and 
grows into the egg. Then a 
part of the living substance 
of the pollen grain unites 





with the living substance of 


the egg. This is called fertili- aay As eltmieen 


zation. of the fertilization 
process. 


It is only after this has 
been accomplished that the egg proceeds to 
grow into the little plant. The fertilized egg 
divides and subdivides and the resulting cells 
grow larger. Subdivision and growth continue 
until a mass of many, many cells is formed. 
The mass changes shape and molds itself into 
the little leaves and bud and stem that consti- 
tute the embryonic plant. Meanwhile the rest 


24 ‘THE THIRD AND FOURTH GENERATION 


of the ovule has also changed; it has developed 
nutritive material and tough coats about the 
plantlet, and so has helped form the seed. The 
ovary enlarges and possibly unites with other 
floral parts to form the fruit (Fig. 4). In 
shelling peas one often sees within the pod, in 





Fic. 4.—Pistil of mandrake enlarging to form the fruit; cross- 
section at the right. 
addition to the fully developed peas, some tiny 
objects, eath attached where you would expect 
a pea to grow; but these are not so large as 
the head of a pin. Such are ovules containing 
eggs that failed to develop because of the lack 
of adequate fertilization. 

It is difficult to watch the egg develop into 
the embryo in the plant, for it is hidden in the 


MALE AND FEMALE 25 


ovary. But the process may be followed with 
ease in the case of the frog’s egg or the toad’s 
egg, easily obtained in spring. The eggs of 
these animals are formed in the ovaries during 
the fall and winter months. They are dis- 
charged by the female frogs in masses almost 
as soon as the ice is gone from the ponds and 
in strings by the toad about a month later. 
When discharged they are spherical bodies as 
large as the head of an ordinary pin, black on 
one side and white on the other. As they lie 
in pond or stream the black side is uppermost. 

The female lays her eggs early in the 
morning, and at the same time the male dis- 
charges into the water the sperm produced by 
glands called the testes. Each sperm is a single 
living cell with a vibratile tail by which it swims 
to the egg. The sperms are so small they can 
only be seen under the microscope. A sperm 
- unites with an egg after the same manner as the 
fleck of living substance from the pollen grain 
combines with the substance of the egg, and it is 
only when this fertilization is accomplished that 
the egg proceeds to grow into the little tadpole. 


26 THE THIRD AND FouRTH GENERATION 


When the eggs are laid each is inclosed in a 
capsule of jelly, so sticky that adjacent eggs 
adhere in masses or, in the case of the toad, in 
strings. ‘The masses are as large as the clenched 
fist of a child and are found attached to grass 
stems, rushes, or twigs in the shallow parts of 
the ponds. Frogs seem to have regular egg- 
laying bees, so that one often finds a peck or 
more of egg masses at one favorite spot. Some- 
times the sedgy margin of a stream will be | 
festooned for rods with floating strings of toads’ 
eggs. But you must be out collecting early in 
the morning if you would catch the eggs by the 
time the first division is accomplished. This 
first plane of cleavage runs from the dark pole 
to the light, and each little black bead separates 
into two that lie in close contact, two adherent 
cells in place of the one (Plate II). In the cold 
ice water of the pond development goes on 
rather slowly, but if the eggs are brought into 
the house in some of the pond water they 
proceed to cleave rapidly as they become 
warmer. ‘Two cells become four in an hour 
or less, four change to eight in still less time, 


PLATE II 





THE DEVELOPMENT OF THE FROG’S EGG 


The upper sixteen figures are in pairs, the left one showing a 
side view, the right a top view, of one stage. Lower left-hand 
figure, a newly hatched tadpole. Above it, an end and side view 
of anearlier stage. At right, a back and end view of stage showing 
developing spinal cord and brain. 


» ae ; 


Lesh aN a Oa Bh 





MALE AND FEMALE 27 


and so the process continues until by night each 
egg may have changed into a little spherical 
mass of perhaps a hundred or more cells. 
Meanwhile this mass of cells is growing larger. 
In the course of a couple of days it elongates 
and one can begin to make out the difference 
between future head and body. In another 
day the little tadpoles begin to wiggle out of the 
jelly, and soon they are swimming about seek- 
ing food. How they grow, develop legs, and 
absorb their tails as they change to the adult 
frog is known to almost every boy and girl, but 
it is a process that is always watched with 
interest. This change from a fishlike creature 
that swims in the water and feeds on vegetable 
matter to an insect-eating, air-breathing animal 
is one of the everyday marvels. The whole 
life-history, briefly outlined above, may be seen 
if a few of the eggs in their jelly are put into a 
quart fruit jar or other convenient dish that is a 
third full of water together with some of the 
green water weeds found growing in the pond or 
stream. When the tadpoles are fairly good sized 
the water should be reduced in amount so it is 


28 Tue THIRD AND FOURTH GENERATION 


only an inch deep, and some clean sand should be 
added, so the animals can wiggle up out of the 
water on to the sand at one side of the dish. 
What has been described in particular for 
the mandrake and the frog is a universal process 
among the common plants and animals with 
which you are familiar. There is a process of 
reproduction among the lower forms of life by 
which the adult becomes two or more young by 
simply dividing into parts, each of which is 
remodeled into a perfect animal or plant, as 
the case may be. But in all higher types it is 
almost universally true that the young are 
produced from eggs which must be fertilized by 
the sperm before they will begin to develop. 
It is evident that the offspring is the joint 
product of the two parents, a union of two 
distinct lines of hereditary descent, and as 
such may manifest characters peculiar to each. 


QUESTIONS 
1. Have you ever found frogs’ eggs or toads’ eggs ? 
Can you describe them ? 
2. Have you found the eggs of other animals, like 
flies or turtles or fish? If so, where? 


MALE AND FEMALE 209 


3. Will you draw from memory some flower you 
know, like the nasturtium or the tiger lily, to show the 
parts of the blossom? Show by the drawing where the 
eggs lie in the flower. 

4. Make a statement to show how important the 
egg is in the life-history of a plant or animal. 

5. What is the importance of fertilization ? 

6. By what process does the fertilized egg grow 
toward the adult individual ? 

7. What is the value of having the new individual 
come from two lines of ancestry ? 


CHAPTER IV 


SOME LAWS OF HEREDITY 


Some of the phenomena of heredity are so 
conspicuous that they are evident to everyone; 
yet they are so commonplace that we pass 
them by without appreciating their significance. 
That like reproduces like is a fundamental con- 
ception in practice as well as in theory. The 
hen is set on a clutch of her eggs with every 
assurance that chickens will hatch. Men do 
not “gather figs of thistles,’’ and that which 
is sown we expect to reap. It is furthermore 
well known that particular traits or features 
may appear as family characteristics. In one 
of the royal families of Europe, the Hapsburg 
family, a prominent jaw and full lips were so 
marked that “the Hapsburg jaw” was almost 
a mark of royalty. Such traits or features may 
occasionally skip a generation to reappear in 
some later member of the family. The child 
may resemble a grandparent or an uncle. 


30 


SOME LAws OF HEREDITY 31 


Breeders have known that stock must be kept 
pure to maintain its valuable characters, but 
new combinations of desirable qualities have 
been achieved by chance rather than by skill. 
It is only within this century that our knowl- 
edge of heredity has advanced from such hazy 
notions to the rudiments of the laws that govern 
the complicated phenomena. 

In the middle of the last century an Austrian 
monk named Gregor Mendel, teacher of science 
in a monastic school at Briinn, became imbued 
with the idea that mankind must have some 
definite knowledge of the laws of heredity as a 
working basis for the improvement of grains 
and fruits, of the breeds of cattle, and even of 
human kind. He decided to experiment with 
garden peas in an endeavor to ascertain these 
laws. He was measurably successful and 
described his results in the Proceedings of the 
Scientific Society of Briinn (1866). The paper 
attracted no immediate attention in the scien- 
tific world, for the volume in which it was 
published was rather obscure and _ biologists 
were just then absorbed in Darwin’s startling 


32 THE THIRD AND FouRTH GENERATION 


theories of the origin of species. In 1900 three 
other investigators, Hugo de Vries, a Hollander, 
Correns, and Tschermak, working independ- 
ently, arrived at much the same results that 
Mendel had reached. In reviewing the litera- 
ture of the subject de Vries unearthed Mendel’s 
publication, and the later discoverers promptly 
gave the credit of priority to Gregor Mendel. 
So the formulated statement of the way in which 
many characters behave in hereditary trans- 
mission is still called Mendel’s law. 

Some pea vines bear peas that are quite 
green when ripe, others produce those that are 
a distinct yellow. Mendel used a plant of each 
of these two sorts as parents, cross-pollinating 
them carefully. The process is now accom- 
plished somewhat in the following way. Just 
before the flower buds are ready to open, some 
of them are opened by hand on each sort of 
vine and the anthers removed. Such blossoms 
are then powerless to discharge pollen on to 
their own stigmas. Small paper bags are 
tied over these flowers so that no other pollen 
can accidentally get to them by wind or 


SoME LAWS OF HEREDITY 33 


insect visitor. When later these buds open 
in the usual way, showing thereby that their 
pistils are ripe and ready for pollination, a 
small brush is touched to the pollen-bearing 
anthers of a normal flower on a vine that will 
bear yellow peas, and then this pollen is dusted 
on to the stigmas of the bagged blossoms on 
the vines that would naturally bear green peas. 
In a similar way the bagged blossoms on the 
vines that would normally bear yellow peas 
are pollinated with the pollen from those bear- 
ing green peas. ‘The bag is removed from the 
flower only long enough to apply the pollen 
with the little brush, and then it is left in 
place so that no other pollen can get on to 
confuse the results. 

When the peas formed in the pods that grew 
from these cross-pollinated parent blossoms 
in Mendel’s experiment, they were all of the 
yellow sort. These were then planted and 
the blossoms on the resulting vines (the chil- 
dren) -were allowed to pollinate freely, just 
as they do ordinarily in the garden. The peas 
that now formed (grandchildren) on these plants 


34 ‘THE THIRD AND FOURTH GENERATION 


were, surprisingly, of the two sorts again, the 
green and the yellow. Moreover, of the 8,023 
peas so produced 2,001 were green, which makes 
the proportion of yellow peas to green peas 
almost exactly 3 to 1. Mendel tried a similar 
experiment with vines that grew about six 
feet tall and dwarfs of only eighteen inches, 
cross-pollinating their blossoms in the same 
careful way. When the resulting peas were 
planted, they produced nothing but tall vines. 
But from the peas that these tall vines produced 
in the usual way grew both tall and short vines, 
and when counted they were discovered to be 
very nearly in the proportion of three tall vines 
to every short one. Similar results were 
obtained with vines that produced smooth peas 
and those that grew only wrinkled ones, with 
vines that bore colored blossoms and those that 
had white ones. A tabulation of Mendel’s re- 
sults with peas differing in these and in other 
characters is found in Table IT. 

Since in all these cases one of the characters 
in each pair seems to eclipse the other in the 
first hybrid generation (known as the F, genera- 


SOME LAWS OF HEREDITY 35 


tion), Mendel designated it as the dominant 
character, while the character that temporarily 
recedes from view he called the recessive. 
When, then, two plants are crossed differing in 
only one particular, the children manifest only 
the dominant character; but the grandchildren 














TABLE II 
Character Number of ‘Number of Recessives| Ratio 
Dominants 
Form of seed...... 5,474 smooth | 1,850 wrinkled 2.96:1 
Color of seed coat .| 6,022 yellow 2,001 green 2.0121 
Color of flowers ...| 705 colored 224 white Reine 
Form of pods...... 882 inflated 299 constricted | 2.95:1 
Color of unripe pod.| 428 green 152 yellow Py ee BG 
Position of flowers .| 651 axial 207 terminal Ae Go 
Length of vine....| 787 tall 277 dwarf 2.84:1 











Note that the greater the numbers involved in any experiment the closer 
the approximation to a ratio of 3:1. 


(F, generation) are of the two types again 
and in the proportion of three dominants to 
one recessive. ‘This does not mean that if, 
in the example first cited above, you should 
find four peas in a pod in the F, generation 
three would be yellow and one green, but it 
does mean that out of 4,000 peas of the 
second generation close on to 3,000 would be 
yellow and 1,q00 green. Darbishire repeated 


36 THE THIRD AND FOURTH GENERATION 


Mendel’s experiment with the yellow-green 
cross, as have others, and obtained 105,145 
yellow peas to 34,792 green in the F, generation, 
a proportion of 3.02 to I. 

When the recessive peas of the second 
generation (the grandchildren) are interbred, 
they are found to give nothing but recessives; 
green peas of this generation gave Mendel 
nothing but greens when planted generation 
after generation; short plants produced only 
shorts. A third of the dominants were found 
to give nothing but dominants, but the other 
two-thirds, when interbred, gave offspring that 
were again of the two types, dominant and 
recessive, and again in the proportion of 3 to I. 
Using the letters D and R to stand for dominant 
and recessive, respectively, Mendel’s law for 
the crossing of two plants or animals differing 
in only this one particular may be diagram- 
atically shown on opposite page. The plants 
of the F, generation (children) are designated 
D (R) rather than just D, although they show 
only the dominant character, because the reces- 


sive character shows up in the next genera- 


SomME LAws OF HEREDITY i 


tion, so that Mendel conceived it must be 


present though hidden. 
D—R 
| 
F, Generation D(R) 
| Mi 
vps nia ® 2 D(R) The 
Cocky at Cie ret Sia aceite 
Ee wy BBP) eet B, 2 D(R) TAR 
eee | alah 
{need B, er Lee Ra ae rc rcs ak 


But now what happened when plants were 
crossed differing in two characters? Mendel 
found, as before, that in the F, generation only 
the dominant characters were apparent, but 
that in the next generation the recessive char- 
acters reappeared. Thus pea plants bearing 
smooth yellow peas were crossed with those 
having wrinkled green seeds, and all the peas 
produced were smooth and yellow. When, 
now, these were planted and the flowers on 
the vines were allowed to pollinate freely in 
the natural way, there resulted peas of four 
sorts and always in a definite ratio, namely, 


38 THE THIRD AND FOURTH GENERATION 


g yellow smooth peas, 3 yellow wrinkled, 3 
smooth green, and 1 green wrinkled. This 
proportion obtained only when large numbers 
were produced. These results of Mendel’s have 
been repeatedly verified since. 

Mendel could hardly have achieved such 
very definite results without devising some 
theory to account for them. He conceived that 
a pea plant producing yellow peas has some- 
thing in its every cell that determines the color 
of the peas to be produced, even in the germ 
cells which fuse at the time of fertilization. 
Each character is determined by the presence 
of a definite substance that acts to produce it. 
When then the egg of a pea plant normally 
producing yellow peas is fertilized by the sperm 
(product of the growth of the pollen grain) of 
such a plant, the fusion in fertilization might be 


represented somewhat thus: 
QO: - @ 
Egg Sperm Fertilized Egg 


When a pea plant producing yellow peas is 
crossed with one producing green peas, Mendel 


SOME LAws OF HEREDITY 39 


thought that the determiners for yellow were 
stronger than those for green, and so a plant 
which contained both would only produce 
yellow peas. The modern explanation is simi- 
lar but simpler, namely, that if a determiner 
for yellow is present in the fertilized egg the 
plant that grows from this will produce yellow 
peas, but if no yellow determiner is present the 
plant will produce green peas. In other words, 
peas are naturally green, but may be yellow if a 
determiner for yellow is added. ‘The case of a 
yellow-seeded plant fertilizing itself would be 
correctly represented above. In the case of a 
yellow-seeded plant crossed with a green-seeded - 
we would have either 


Q+0-@ 


Egg Sperm Fertilized 
Egg 
or 
Egg Sperm Fertilized 


$24 
In either case the result is the same. The 
fertilized egg has in the cross a single dose of the 


40 ‘THE THIRD AND FOURTH GENERATION 


determiner while in the self-fertilized yellow- 
seeded plant diagrammed above it has a double 
dose; in both instances a yellow-seeded plant 
is the product, but one has all its cells provided 
with a single yellow determiner, the other has 
cells with two determiners. 

Mendel further supposed that at one stage, 
when the cells of the plant divide to produce 
those cells known as the eggs and sperm that 
are so essential in reproduction, the determiners 
remain indivisible. It is evident that when a 
mother-cell divides to produce two daughter- 
cells that are to function as eggs or sperm, if 
- the mother-cell has two determiners each egg or 
sperm may have one; if, however, the mother- 
cell has only one determiner, the sperm or eggs 
must be of two sorts, one with and one without 
the determiner. The pure yellow-seeded pea 
plant would have eggs and sperm each possess- 
ing a determiner for yellow (Y). The pea 
plant resulting from a cross of the yellow-seeded 
and the green-seeded would have eggs and 
sperm both with and without the yellow 
determiner and these two kinds in equal num- 


SoME LAws or HEREDITY 4I 


bers. It is a matter of chance which sort of 
sperm will fertilize either sort of egg when these 
hybrid offspring shall produce their progeny. 
The possible combinations in such an event are 


portrayed in the following scheme: 





The results are one fertilized egg with a 
double dose of the determiner, two that have a 
single dose, and one that has no yellow deter- 
miner. Now since the presence of the yellow 
determiner makes the plant yellow-seeded even 
if present in only a single dose we should expect 
the Mendelian ratio of three yellow-seeded 
plants to one green-seeded in the F, generation. 
It is also plain why the green-seeded plants only 
produce green-seeded offspring, for they have 
no yellow determiner in them. It is also 


42 ‘THE THIRD AND FouRTH GENERATION 


evident that one-third of the yellow peas of this 
generation will produce yellow-seeded plants 
only, for they have two determiners in the 
mother-cells that give rise to eggs and sperm, and 
so these will each have the yellow determiner. 
The proportions of the resulting peas in a 
cross between a smooth yellow pea and one 
producing wrinkled green peas are obtained in a 
similar way. The plants of the F, generation 
are represented by SY, and both smooth and 
yellow are dominant characters. The sperm 
and eggs may (1) contain S and Y, (2) only S, 
(3) only Y, (4) neither S nor Y. The possible 
combinations are shown in the diagram on p. 43. 
Nine combinations contain both S and Y, three 
only S, three only Y, and one neither S nor Y. 
Therefore in the F, generation the proportion 
must be the Mendelian ratio, 9-3-3-1. 
Mendel’s law holds good with other forms, 
both animal and plant, quite as well as with 
peas. If, for instance, pure black guinea 
pigs are crossed with whites, the children are 
all black; the grandchildren are three-fourths 
of them black, one-fourth white. The whites 


SOME LAws OF HEREDITY 43 


of this generation are pure recessives and only 
give white when interbred. One-third of the 
blacks are pure dominants and give when 
mated only black offspring; but the rest are 





hybrids and give again, when interbred, three 
black to one white. It does not follow that 
because white is a recessive in guinea pigs it 
will always be such. Thus if a white leghorn 
chicken is crossed with a black minorca the 
children are all white, the grandchildren three- 
fourths white, one-fourth black. In this case 


44 ‘THE THIRD AND FOURTH GENERATION 


white is evidently dominant. Whether a given 
character will behave as dominant or not 
can only be told by trying it out by actual 
breeding. 

Dominance may often be only partial, 
possibly it is never absolutely complete. The 
crossing of white and black Andalusian fowls 
is a case in point. The children, instead of 
being either black or white are black diluted 
with white, called by the chicken fancier a 
“blue.” Of the grandchildren one-fourth are 
pure black, one-fourth pure white, and one-half 
“blue” hybrids. Similarly, when red and white 
four-o’clocks are crossed the children are all 
pink blossomed; neither red nor white is com- 
pletely dominant. The grandchildren are one- 
fourth pure red, one-fourth pure white, and 
one-half pink. 


QUESTIONS 


1. What do you mean by heredity ? 

2. How did Mendel go about it in his work with 
peas to make sure of crossing two varieties so as to get 
a hybrid ? 


SoME LAwS OF HEREDITY 45 


3. State Mendel’s law as it applies to the offspring 
of the cross between smooth and wrinkled peas, carrying 
the matter as far as the great-grandchildren. 

4. The hybrid peas will produce what sorts of egg 
and sperm, and what four possible combinations may 
there be in the fertilized eggs that will grow to new 
seeds ? 

5. Can you find other instances of the working of 
Mendel’s law besides those given? Possibly you have 
raised pigeons or corn, and can give illustrations of 
some of the matters discussed from your own experience 
in crossing different varieties. 

6. Will some members of the class undertake to 
try out a cross with some animals or plants so as to 
illustrate Mendel’s law with actual materials which the 
class may see ? 


CHAPTER V 
MAN A CREATOR 


It is very evident from even so elementary a 
discussion of the matters involved in Mendel’s 
law that at least some hereditary characters 
are pretty definite things which when once in a 
stock remain in it persistently. Yet by appro- 
priate hybridizing of unlike stocks the groups 
of characters that have been united for genera- 
tions may be shaken apart and reunited in new 
combinations. ‘This possibility was recognized 
before the world generally knew of Mendel’s 
law, but it was looked upon as a chance phenom- 
enon; the successful breeder of race horses, for 
instance, was thought to be a good guesser, a 
skilful juggler, but it was scarcely deemed that 
there was any scientific basis for his procedure. 
The work of a few such breeders was so uni- 
formly successful that it was undoubtedly 
founded on some of the fundamental con- 
ceptions of hereditary transmission, even if the 


46 


MAN A CREATOR 47 


men themselves were not conscious of their 
scientific foundations. But with the recog- 
nition of the significance of Mendel’s law, the 
breeder went to work to produce desirable 
modifications of existing animals and plants, 
so that they would more completely serve men’s 
purposes. It seems worth while at the outset 
to get some clear notions of what has been done 
by breeders in their efforts to obtain new types 
of animals and plants, both by those who 
worked in the dark before the laws of heredity 
were at all known and those who are working 
now with better scientific foundations. 

The origin of many domestic breeds and 
races, both of plants and animals, is obscure. 
We are not sure whether the dog is derived 
from one particular species of the wild dogs, 
like the wolf, or hyena, or if the several races 
that we know today are hybrids of several 
species of wild ancestors. The dog has been 
man’s companion from earliest time. As soon 
as we find man’s fossil bones along with his 
crude implements we find also the bones of the 
dog. He was domesticated so early that we 


48 THE THIRD AND FOURTH GENERATION 


have no record of his real origin. While we 
think the chickens of today are probably 
derived from the jungle fowl of India, the many 
sorts of pigeons from the common rock pigeon, 
European cattle from the wild cattle that still 
inhabit some of the game preserves of England 
and Germany, yet it is a matter of probability, 
not of certainty. 

F ortunately ‘the incidents regarding the or- 
igin of certain breeds and varieties are known, 
and such are illuminating. In the first place 
many of the valued domesticated plants and 
animals have been transplanted from the wild 
quite recently. The turkey, for instance, is an 
American bird, the wild turkey still roaming the 
forests in some of the wilder sections. It has 
suffered little change apparently in the process 
of domestication. The same may be said of 
the duck (the common sort being an almost 
unmodified wild mallard), of some pheasants, 
and of the ruffed grouse, lately added to the list 
of domesticated animals. Recently the blue- 
berry has passed under cultivation. The culti- 
vated sort is much: larger, juicier, and more 


MAN A CREATOR 49 


prolific than its wild parent form; yet the 
changes seem to have been induced merely by 
putting it under the more favorable environ- 
ment in cultivation. The Concord grape 
achieved its present size and lusciousness at 
once on being brought into the garden from the 
wild. It is quite evident, then, that men may 
bring animals and plants under domestication 
either with or without producing marked 
changes in them. It is to be noted that after 
they are changed they revert to their wild 
condition again when returned to the state of 
nature. 

In 1791 there was born on the place of a 
Massachusetts farmer named Seth Wright a 
queer-looking lamb with short bowlegs and 
a long sagging body like a dachshund. Now 
Seth Wright had been much annoyed by his 
sheep jumping pasture fences. With true 
Yankee insight he recognized the value of this 
bandy-legged lamb; it might become the 
progenitor of a breed that could not hurdle even 
a low fence, and high rail fences were built only 
with effort. To make a long story short, 


50 ‘THE THIRD AND FOURTH GENERATION 


Wright did produce a breed of sheep, the 
Ancons, by mating this ram to its own off- 
spring, and so inbreeding for several generations. 
The Ancons were long a favorite breed, until 
replaced by sheep with much finer wool. 

In 1889 there appeared suddenly in a herd 
of Hereford cattle at Atchison, Kansas, an 
animal without horns. This single animal was 
the founder of the race of polled Herefords. 
Among some orange seedlings brought to the 
United States by the Department of Agriculture 
from Bahia, Brazil, and planted in California, 
was one that when mature produced the peculiar 
seedless orange now commonly known as the 
navel. From this single tree cuttings have 
been taken to start others, and in this manner 
there have been derived from the one original 
tree all our orange trees that bear navels. 

Note that the short-legged sheep did not 
arise by the selection of gradually shorter and 
shorter legged sheep, the hornless cattle by the 
gradual disappearance of the horns, or the 
navel orange by the slow elimination of seeds 
until the vanishing point was reached; but in 


MAN A CREATOR 51 


each case the new variety suddenly put in its 
appearance in its perfect condition. All the 
breeder had to do was to recognize the value 
of the new type. 

The truck-garden region about Chicago is 
the greatest cabbage growing area in the world. 
Many of the farmers of northwestern Indiana, 
northern Illinois, and southern Wisconsin have 
devoted themselves exclusively to this one crop. 
Within a generation, however, the region has 
been invaded by a very serious disease, the 
‘“vellows,”’ that attacks the young plant, 
withering and killing it. Fields that formerly 
produced tons of cabbages now yield abso- 
lutely none, and the virus seems to remain 
persistently in the soil even after other crops 
have been grown for several years. ‘The plant 
pathologist of the University of Wisconsin was 
called in to help solve the trouble. The 
situation was studied for several years without 
avail. ‘Then in the midst of a fifteen-acre field 
two lusty cabbage plants were found with well- 
formed heads, although all their companion 
plants had succumbed to the dread disease. 


52 THe THIRD AND FouRTH GENERATION 


It seemed to the farmer a pitifully small crop, 
but to the expert a very hopeful one—two 
plants, at least, that were disease-resistant. 
Seed reared from these produced similar healthy 
cabbages on farms that had been unable to 
get a crop with the ordinary cabbage seed for 
years. And now with this new disease-resist- 
ant variety the region is returning with assur- 
ance to its very profitable industry. 

Many other instances might be cited of the 
sudden appearance of new breeds of animals 
or new varieties of plants. Such have been 
long known and have been called “sports.” 
Hugo de Vries, a Holland botanist, obtained 
seed of an evening primrose, at one time prob- 
ably a native of Southwestern United States. 
He planted acres of this “weed” in his experi- 
mental garden near Amsterdam. He dis- 
covered that among thousands of plants which 
bred true to the original primrose, Oenothera 
lamarckiana, there also appeared plants so 
unlike as to be evidently new species, and these 
bred true. There was one with flowers double 


the size of those of the parent species. The 


MAN A CREATOR 53 


plants differed in other respects, too, but this 
was the most conspicuous dissimilarity: it was 
named Oenothera gigas. One had the veins of 
the leaves and the tips of the flower buds tinged 
deeply with red, and was named O. rubrinervis. 
These are but samples of the “sports” that 
were appearing under the very eyes of an 
expert scientist; de Vries.gave to such forms 
the name of mutants and claimed that such 
mutations or saltations have been exceedingly 
important in the evolution of the higher types 
of animals and plants from their simpler 
predecessors. New types of plants and animals 
may appear, then, out of a clear sky, so to 
speak. These mutants breed true. The dif- 
ference between them and the parent form may 
be great or relatively slight, but they unerringly 
perpetuate themselves. 

No American has been more successful in 
producing new varieties of plants than has 
Luther Burbank. He has worked largely 
through the process of hybridization, achieving 
almost by intuition what the scientific breeder 
gets by careful study. Burbank undertook 


54 THE THIRD AND FOURTH GENERATION 


to improve the florist’s daisy. The common 
American daisy, a weed in many sections of the 
country, is exceedingly vigorous and is a free 
bloomer, but neither the squatty form of the 
plant nor the dirty white blossom cluster makes 
it particularly attractive. The English daisy 
has a blossom cluster that is much larger, and 
the plant is of fine upright habit, but it is rather 
delicate, demanding sheltered situations. The 
Japanese daisy has small flower clusters, but 
these are of a wondrous pearly luster. Burbank 
conceived the project of combining the hardi- 
hood and free-blooming quality of the American 
species, the fine habit and large size of the 
blossom cluster of the English species, and the 
luster of the Japanese. He cross-pollinated 
two of these and then bred the hybrid plants 
with the third species and succeeded in achiev- 
ing the desired combination. The new daisy 
he called the Shasta daisy. 

Burbank’s potato, produced early in his 
career and sold to an eastern seed man for 
one hundred and twenty-five dollars, is esti- 
mated by the United States Department of 


MAN A CREATOR 55 


Agriculture to be adding to the wealth of the 
nation by its increased productivity some 
seventeen millions of dollars annually. ‘These 
are but a few instances of his many successes. 

Burbank hybridizes by wholesale rather 
than by wise forethought and takes his chances 
on getting the hoped-for union of characters. 
His skill seems to consist in judging what 
seedling plants in thousands have the combina- 
tion of desired characteristics in such form that 
their progeny will perpetuate them. Such a 
method frequently entails the destruction of 
acres of hybrids that do not manifest a valuable 
reunion of features. Burbank’s remarkable 
knack of achievement has been duplicated, by 
other experimenters who are more scientific in 
their methods and strictly dependent on the 
advance made in our knowledge of the law of 
heredity. 

A few years ago the prairie lands of the 
Canadian Northwest territories were thrown 
open to settlers. It was soon discovered that 
these fertile lands were capable of producing 
enormous wheat crops, quite equal to those 


56 ‘THE THIRD AND FourTH GENERATION 


that made such states as the Dakotas famous. 
There followed a great exodus of American 
farmers, from the border states particularly, 
into these promising lands. Within a few 
years, however, most of these adventurers 
came back to the States, for the early frosts of 
the new territory often nipped the unripe grain 
and spoiled the harvest. Not infrequently, too, 
the heavy gales common on these northern 
prairie lands blew down the grain in late 
summer, before it was ripe, making it well-nigh 
impossible to harvest it. Canadian farmers 
sent to the scientific breeders an insistent 
demand for a new type of wheat, one with the 
desirable hardness (the American miller likes 
no other), with the large yield of the prolific 
brands, but also one that would ripen early 
and that should have an exceptionally strong 
stalk to stand up against heavy winds. These 
qualities were all known, but in no one wheat. 
Thus Red Fife, a Russian wheat coming to 
America by way of Germany and Scotland, is 
hard and a high yielder. An Indian variety 
possesses the short sturdy stems, though it is 


MAN A CREATOR ys 


late. But the breeders went to work by a pro- 
cess of hybridization and selection, based on 
Mendel’s law, to unite the needed qualities in 
one variety, and they succeeded so well that in 
three years’ time they could begin to send the 
farmers small amounts of seed that met the re- 
quirements. Now these great prairie provinces 
are producing regular and dependable crops. 

It was long taken for granted that improve- 
ment could be effected in a herd of animals or a 
plant crop by selecting from the general run of 
individuals the best ones to use for continued 
propagation. Thus the farmer went through 
his field at harvest time and picked out the 
largest heads of grain and those with the 
heaviest kernels to use as seed for the ensuing 
year, hoping that this process, repeated: year 
after year, would increase the yield of his land- 
The chicken fancier selected the hens that 
produced the largest number of eggs to use as 
breeders, in the hope that the egg production 
of the flock would gradually rise. But this sort 
of mass breeding was found to yield very 
unsatisfactory results. Galton had discovered 


58 THE THIRD AND FOURTH GENERATION 


years before that the children of two very tall 
individuals are not likely to be as tall as the 
parents; the same tendency to return to 
mediocrity is seen in the children of very short 
parents. Johannsen found similarly that if 
you plant large beans in a garden where cross- 
pollination is certain, the offspring are prone 
to be of less size on the average, but if you plant 
a single large bean and let the blossoms on this 
plant self-fertilize, the beans so produced are 
very like the parent in size. That is, pure-line 
stock is true to its type. Nilsson, the famous 
director of the Swedish Experimental Station 
at Svalov, found that the wheat produced 
by planting the kernels of a _ single head 
was remarkably uniform, displaying only the 
parental qualities; but if seed from a number of 
heads, all equally good to the eye, were sown 
in the experimental plot, the resulting grain 
was not at all uniform. Some might be good, 
much indifferent, and some really bad. Nilsson 
conceives that such grains as our oats and wheat 
are resultants of the blending of many strains, 


and that these separate out constantly, appear- 


MAN A CREATOR 59 


ing more or less pure on individual plants. An 
ordinary crop is therefore an assemblage of 
many varieties. Only as you succeed in pro- 
ducing seed of a single variety will the crop 
raised be uniform or dependable. He therefore 
undertook to establish a number of these pure- 
line or pedigree cultures and find out by 
experimental planting in various locations which 
one was best adapted to yield large crops in a 
particular soil and particular climate. So he 
has been able to furnish the farmers of Sweden, 
working under the very diverse conditions that 
exist there, the particular types of wheat or 
oats that best fit their needs. Often it is 
necessary to hybridize two or more varieties 
and establish the right combination of desirable 
qualities by selection, but this is a relatively 
simple matter when pedigree cultures are at 
hand, each breeding true to one or more of the 
characters needed. 

Our cultivated wheat was derived from a 
wild plant similar to, if not identical with, one 
‘discovered recently growing like grass in the 
rock crevices and sparse soil of the rougher 


60 THe THIRD AND FOURTH GENERATION 


portions of Palestine. Strangely enough our 
European strains of wheat will not stand these 
very conditions of drought that maintain so 
commonly in the semiarid region where the 
wild progenitor thrives. Apparently man has 
selected it through these many ages for maxi- 
mum yield under the most favored conditions 
of soil and moisture, so that its hardihood has 
disappeared. It is now a pampered weakling. 
We lose half our cereal crop by drought. It is 
hoped that some of the sturdiness of the original 
stock may be bred into modern strains of wheat 
by hybridization, so there may be produced a 
wheat of high productivity that will grow even 
in arid regions. It would add enormously to 
the value of some of our western lands where 
the rainfall is slight if such a crop could be 
assured. The Indians of the Southwest have 
achieved such a result with corn, and the corn 
of the desert tribes is a marvel of adaptation, a 
dwarf plant with small leaf surface but a large 
area of shallow roots to absorb the dew and 
light showers, and a single ear that is very rena, 
considering the size of the plant. 


MAN A CREATOR 61 


No less remarkable is the variety of types 
of corn that civilized man has produced to suit 
his needs. If corn is raised for the purpose of 
manufacturing cornstarch, a variety that has 
a high percentage of starch is sown; if it is to be 
fed to beef cattle, it must be a sort that is rich 
in protein; if hogs are to be fattened, the oil 
content must needs be large; if it is to be used 
as a table vegetable, it must possess a large 
percentage of sugar. No sooner is a new use 
discovered for corn than the breeder develops a 
variety to suit it. Then, too, the yield per acre 
has been enormously increased, in part by 
better methods of cultivation, but in part also 
by improving the type of corn plant. The ideal 
plant is one with a strong, well-buttressed 
stalk, with two large ears, that will stand up 
even in heavy winds; it must possess broad yet 
firm leaves, for the manufacture of the materials 
that go into the grain occurs in the leaf. The 
ears should be long and thick without too large 
a cob, the latter well covered even over the tip 
and butt with straight rows of long even kernels 
that fit together without waste spaces (Fig. 5). 


62 THe THIRD AND FOURTH GENERATION 


A single ear of such seed corn has sold for hun- 
dreds of dollars. 

It must be recalled that at the top of the corn 
stalk there appears what is usually called the 





Fic. 5.—A good ear of corn. Note the close-fitting kernels 


“tassel,”’ really a cluster of blossoms that bear 
only stamens. Such separation of the stamens 
and pistils on different blossoms is quite 
common in plants that depend on the wind to 


MAN A CREATOR 63 


carry their pollen; grasses, sedges, and many 
trees like the willows and poplars are familiar 
examples. There protrudes from the young 
ear the bunch of silk, each thread of which is a 
style, its tip a stigma of one pistil. The ovary 
contains one ovule and after fertilization it 
develops into a single kernel of corn; there are 
as many pistils and of course as many silks as 
there are kernels in the ear. If two or more 
kinds of corn are planted in the garden and these 
tassel out at the same time, the kernels in the 
ears may be in part or entirely hybrids. When 
Mexican black corn and ordinary varieties are 
planted together, some kernels‘ on the ear will 
be black, some white, depending on whether 
they are hybrids or not. 

Since it has been found impossible as yet to 
get any one corn that has all the desired 
qualities in it and that breeds true, the farmer 
often has recourse to planting in alternate rows 
‘two varieties, each with some of the desirable 
qualities, so that they will cross-pollinate and 
the resulting hybrid kernels, it is hoped, will 
have most of the desired qualities. 


64 ‘THE THIRD AND FOURTH GENERATION 


In recent experiments conducted at various 
state experiment stations to produce strains of 
chickens with increased egg-laying ability, it 
has been found that it is not only necessary to 
select as a breeder a hen that lays well, but 
that her offspring must be good layers too. 
In other words, the breeder must have proof 
that the animal has the power to transmit her 
desirable quality or, as he says, is prepotent. 
It is by close inbreeding with such stock 
that the two-hundred-egg-a-year hen has been 
developed. 


SUMMARY 


The breeder hopes to discover animals and 
plants in the wild state that may serve mankind 
well when domesticated, and he expects that 
some at least will be improved merely by 
domestication. He is on the lookout for sports 
or mutants that show valuable new characters; 
these he adopts and conserves. He makes new 
combinations by hybridization and watches for 
complex varieties to separate into their com- 
ponent strains so as to start valuable pedigree 


MAN A CREATOR 65 


cultures. By close inbreeding he prevents the 
dilution of valuable traits. 


QUESTIONS 


1. Can you see any reasons why it is likely that 
the dog is the result of crossing several different species 
of wild ancestors rather than being the derivative of 
only one of them? Can you think of any other 
domesticated animals other than those given that are 
little changed by man’s adoption ? 

2. Itis quite possible to find in the literature many 
illustrations of domestic breeds arising as sports; will 
you add to the few given ? 

3. Are there disease-resisting plants other than the 
cabbage; can you find out how they arose? Are there 
disease-resisting races of men ? 

4. What was Hugo de Vries’s contribution to our 
discussion of heredity ? 

5. Will someone look up and report the way Bur- 
bank produced his plum cot, stoneless prune, and 
royal walnut ? 

6. Do the farmers or gardeners in your vicinity 
practice mass breeding or pure-line breeding ? 

7. Will you estimate the value of the work of 
Nilsson of the Swedish Experiment Station ? 


CHAPTER VI 
THE VISIBLE BASIS OF HEREDITY 


As we have seen in a preceding chapter, 
when the eggs of the frog are shed into the 
water by the female, the male at the same time 
discharges the sperm on to them. The pair of 
frogs then pay no more attention to their 
eggs. Such fertilized eggs have no connection 
with the bodies of their parents, so that what- 
ever hereditary characters are displayed by 
the young frogs must evidently be trans- 
mitted entirely through the eggs and sperm. 
A similar situation obtains among many of 
the lower plants and a majority of animals; 
the egg develops entirely dissociated from the 
parent. While in the higher animals the egg, 
during its development, is held in one of the 
reproductive organs of the mother (the womb 
or uterus), the connection of the growing 
embryo with the parent is not as close as at 
first appears; no blood flows from the parent 

66 


THE VISIBLE BASIS OF HEREDITY 67 


to the young, nor is there any nerve connection 
between the two. It is no wonder, then, that 
the prying eye of the microscope has been turned 
upon these reproductive cells, the eggs and 
sperm, to see if there can be discovered in them 
anything that may be regarded as the carriers 
of the hereditary characters. Certain structures 
have been discovered which many scientists 
believe do constitute a visible physical basis of 
heredity. 

The term “‘cell”’ applied to the egg is rather 
unfortunate, for it calls up a vision of an empty 
space surrounded by walls. The cells that 
make up the animal and plant are, on the 
contrary, masses of protoplasm, each usually 
bounded by a layer of substance, the cell wall, 
that is formed by the protoplasm; within each 
cell is a small dense mass of protoplasmic 
material, the nucleus, that is quite essential. 

Protoplasm is a somewhat jelly-like mate- 
rial, almost transparent, sensitive, contractile, 
capable of taking in and using certain food 
substances to build new protoplasm. The 


term is a collective term, somewhat as “‘society””’ 


68 THe THIRD AND FourTH GENERATION 


is; it stands, not for a single substance, but for 
a group of related substances. It is the physical 
basis of life, that in which life inheres; the living 
part of animal or plant is always protoplasm. 
It is by no means invariable; quite the con- 
trary, it probably has a different composition 
for each species of animal or plant, perhaps for 
each kind of tissue. The protoplasm of the cell 
is differentiated and its parts serve a variety 
of purposes. The nucleus functions differently 
from the cell body; the chloroplasts of the 
plant cell that give it the green color serve to 
make the sun’s energy available for the manu- 
facture of plant foods. Various foreign sub- 
Stances may be held in the protoplasm and at 
times be almost indistinguishable from it; such 
are the food materials in process of elaboration 
or the waste matters that are on the way to 
excretion. | 

After fertilization, it will be remembered, the 
egg cell proceeds to divide and subdivide, form- 
ing a mass of cells that gradually transforms 
into the embryo and that finally grows, by con- 
tinued cell division and differentiation, into the 


THE VISIBLE BASIS OF HEREDITY 69 


adult (Plate II, p. 26). Cell division at times 
may be a very simple process. The nucleus 
elongates, becomes dumb-bell shaped, and 
pinches apart to form two new nuclei. The cell 
body goes through a similar performance, and 
each new nucleus lies in one of the new cells. 
But in most cases cell division is much more 
complicated. The physical condition of the 
cell protoplasm varies much; at times it is fluid, 
again gelatinous, and it may assume a fibrous 
or spongy structure with fluid materials in the 
meshes or spaces. As the nucleus prepares for 
division its substance assumes this latter con- 
dition. At the points of juncture of the fibrous 
strands there are found granules that stain 
very deeply with certain chemical substances; 
this deeply staining material has hence been 
called chromatin. As the early division stages 
come on in the cell the spongy network becomes 
coarser and the chromatin granules unite to 
form larger grains (Fig. 6, B and C). Many 

strands of the fibrous mesh break, others appear | 
to contract and draw the grains of chromatin 


closer together until finally this nuclear material 


70 THE THIRD AND FOURTH GENERATION 


appears as a number of rodlike, ovoid, or other 
characteristically shaped bodies now known 
as chromosomes. Meanwhile the boundary of 
the nucleus has disappeared and the chromo- 
somes have come to lie in one plane in the 
mid-region of the more or less spherical cell, des- 
ignated the equatorial region (Fig. 6, F). Now 
each of the chromosomes divides into equivalent 
parts. Not infrequently the division begins 
before the component chromatin grains fuse, 
and then it is apparent that each tiny granule 
divides so that each daughter chromosome 
receives one-half (Fig. 6, E). The daughter 
chromosomes move toward the opposite poles 
of the cell and fuse (Fig. 6, G and H). This 
solid mass gradually becomes porous as the 
meshwork reappears. New nuclear walls are 
formed. Between the two new nuclei the cell 
lays down a new cell wall and what was one cell 
has thus become two (Fig. 6, I). 

The whole process impresses one as a device’ 
for insuring the equal distribution of the 
chromatin materials to the daughter-cells. If 
this chromatin is the real bearer of hereditary 


THE VISIBLE BAsiIs oF HEREDITY vt 


qualities, its equal partition is significant, for 
each cell must have its share of the fundamental 





Fic. 6.—A cell dividing, showing behavior of chromosomes 


substance peculiar to the plant or animal. Such 
a precise method for dividing the chromatin is 


72 ‘THE THIRD AND FouRTH GENERATION 


one weighty reason for believing that it is the 
physical basis of hereditary transmission; other 
reasons follow. ‘The sperm consists of a head 
made almost exclusively of chromatin, and of 
a middle piece, and tail that propels the sperm 
to the egg. These parts are often dropped at 
time of fertilization, so that only the head unites 
with the egg. Yet the plant or animal resulting 
from the fertilized egg may show quite as many 
hereditary traits derived from the father’s 
ancestry as from the mother’s; these evidently 
must have been brought into the egg by the 
chromatin. Boveri was able to shake the 
nucleus out of certain large sea-urchin eggs and 
then fertilize these denucleated eggs with the 
sperm of another species. When these eggs 
developed they showed the specific characters 
of the latter only; none of the characteristics 
of the species from which the eggs were derived 
were apparent. He also found that under 
exceptional conditions, when sea-urchin eggs 
were fertilized with sperm of the same species, 
two or even more sperms would enter the same 
egg. Then the chromosomes are distributed 


THE VISIBLE BASIS OF HEREDITY 73 


to the cells as they form, in a very erratic 
manner, and the resulting embryos are highly 
abnormal, presumably because the hereditary 
determiners have gone astray. 

The cells of any species of animals or plants 
always contain a specific and constant number 
of chromosomes except as noted below. The 
number may vary greatly in different animals 
and plants; thus a biologically famous little 
fruit fly (p. 81) has four, the mosquito, Culex, 
has six, the rat sixteen, the frog twenty-four, 
and a white man forty-seven. In radiolarians 
it is claimed the number is about 1,600. There 
is a similar wide variation in the number of 
chromosomes found in plant cells. There is no 
connection between the number of chromosomes 
and intimacy of relationship; animals widely 
separated in the animal kingdom may have the 
same number; those very closely related may 
have an unlike number. 

It is very evident that if the egg of an animal 
contained the regular number of chromosomes 
and the sperm brought in as many more at time 
of fertilization, the new animal developed from 


74 [HE THIRD AND FOURTH GENERATION 


the fertilized egg would have twice as many 
chromosomes as either parent. This doubling 
process would continue generation after genera- 
tion and soon give us an incalculable number. 
During the production of the eggs and sperm 
from the germ mother-cells in most animals, 
and in the production of the spores from the 
spore mother-cells in plants, there is one 
division when, instead of the usual number of 
chromosomes appearing in the equatorial plate 
(Fig. 7, F), only half that number appears, but 
these are apparently double chromosomes. 
When they divide to form the new nuclei, the 
chromosomes that form the doublets go to 
separate cells. By this ‘‘reduction” division in 
place of the customary “equation”’ division the 
daughter-cells have unlike chromatin material. 
Thus if we number the chromosomes 1, 2, 
3, 4, then the equation division would give to 
each daughter-cell one-half of each; but the 
reduction division might give to one daughter- 
cell any two, as 1 and 3, and to the other 
daughter-cell the others, 2 and 4. When the 
egg and sperm come together in fertilization, 


THE VISIBLE BASIS OF HEREDITY 75 


the half-number (haploid number) in each unite 
and make up the usual (diploid) number once 
more. ‘This takes place in animals usually very 
soon after the reduction division has occurred; 
but in plants the union may be long delayed, 
for the spore does not at once produce the germ 
cells, but the sporophyte, whose tissue then 
consists of cells with the haploid number of 
chromosomes. 

There is very good evidence that even when 
these chromosomes seem to lose their identity 
in the newly formed nuclei they really do not. 
When, for instance, two animals of similar but 
still unlike species, such as different sorts of 
minnows, are used as parents, the chromosomes 
in the germ cells are of such different shapes that 
they can be recognized in the equatorial-plate 
stage of the successive divisions of the fertilized 
egg and even in the divisions of tissue cells in 
the well-developed young fish. In some plant 
cells the swollen and alveolar chromosomes can 
be distinguished apparently even in cells that are 
in the resting stages. Biologists are inclined to 
believe that chromosomes retain their identity, 


76 ‘THE THIRD AND FOURTH GENERATION 


although in many cases we as yet have no 
visible demonstration that such is the case. 

If we letter the chromosomes in the ancestors 
of an individual so we can keep track, generation 
aiter generation, of certain ones, we might have 
some such scheme as the following to represent 
the source of the chromosomes in the individual. 
For the sake of simplicity it is assumed that in 
the particular animal considered there are only 
two chromosomes in the body cells. The 
squares and large circles represent the individ- 
ual animals, male and female, respectively; 
eggs and sperm are represented by conventional 
small circles and tailed figures. The cells of 
the individual animal, one of which is repre- 
sented in the lower row of the diagram, were 
derived from the fertilized egg by its repeated 
cleavage. This cell, as all of its fellows, contains 
two chromosomes designated b and 0; b comes 
from the egg, o from the sperm, which of course 
were derived from the mother and father, 
respectively. Similarly, the mother’s cells with 
chromosomes 6 and f were derived from a 
fertilized egg, the unfertilized egg contributing 


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78 ‘THE THIRD AND FOURTH GENERATION 


the chromosome 0, the sperm f. Tracing back 
the source of the chromosomes thus step by 
step, 1t is evident that the two chromosomes 
in the cells of this particular individual whose 
ancestry is diagrammed were derived one from 
a great-grandmother, one from a great-grand- 
father, and they might in a similar way be 
traced back much farther. If now a given 
chromosome contains a set of determiners for 
particular characters we can readily see why 
this individual bears striking resemblance to 
two of its great-grandparents. This, of course, 
is a crude illustration of the sort of thing that 
inheres in the notion of the individuality of 
the chromosomes. It must not be taken for 
granted that all of this has been proven; it is 
merely a working hypothesis rendered probable 
by recent investigations and the experience of 
breeders. 

The first successful attempt to connect 
specific characters with particular chromosomes 
came with the discovery that in certain insects 
there is one chromosome in the male called the 
odd or x-chromosome which does not pair with 


THE VISIBLE BASIS OF HEREDITY 70 


a fellow preparatory to the reduction division 
at the time the sperm are formed. It goes 
entire to one or the other. of the sperm so that 
these are of two sorts, one with the odd chromo- 
some, one without it. It was Henking who 
made this discovery in 1899 in a locust or 
grasshopper, Phyrocorrus; it was soon con- 
firmed by other investigators working on other 
animals. McClung, the same year, suggested 
that this odd chromosome is a sex-determiner. 
If an egg is fertilized by a sperm that contains 
the odd chromosome, the fertilized egg develops 
into a female, but if fertilized by a sperm of the 
other type it develops into a male. Thus in the 
white man there are forty-seven chromosomes 
in the male, but forty-eight in the body cells of 
the female. Evidently the chromosome which 
is an odd one in the male finds a mate in the 
cells of the female since the chromosome number 
is even. The female may be said to have a 
double dose of the sex chromosome, the male a 
single dose. Representing the haploid number 
of chromosomes by 7 the formula for the cells 
of a female is usually given as 2u-+2, for the 


80 THE THIRD AND FouURTH GENERATION 


male 2v-+1. Each egg would have n-+1 chro- 
mosomes. ‘The sperm will be of* two sorts, 
those containing  .chromosomes and _ those 
having m-+1. If an egg is fertilized by the 
latter sort of sperm it will produce a female 
(2n+2); if by the former a male (2-+1). 
Since the chances are equal that a sperm of one 
sort will find eggs to fertilize as often as will 
those of the other type, the number of males 
ordinarily equals the number of females. In 
some animals in which one sex greatly out- 
numbers the other it has been shown that there 
is a very high mortality among the sperm of one 
type. 

Biologists are not agreed that the odd 
chromosome is really the sex-determiner; it 
may merely be a sex-indicator. But at any 
rate there is established a specific relation | 
between a very conspicuous character, sex, and 
the presence of a particular chromosome (or, at 
times, group of chromosomes). This relation 
has been found to obtain in a very great 
variety of animals. Recent work tends to show 
that the original impulse toward one or the 


THE VISIBLE BASIS OF HEREDITY SI 


other sex due to the presence of the sex chromo- 
somes is only one factor in the final outcome, 
though it is probably the most important. 

Professor Morgan, of Columbia University, 
who has for many years been conducting experi- 
ments on inheritance in the fruit fly, Drosophila, 
finds that the hereditary characters behave as if 
they were bound together in four groups—one 
large group, one with very few characters in it, 
and two that are intermediate. Now Droso- 
phila has four chromosomes in its cells—one 
very large one, one quite small, and two of 
intermediate size. Dr. Morgan thinks that this 
is more than a coincidence. His work tends to 
show, not only that a specific character is located 
in a particular chromosome, but that the de- 
-terminer for the character is located at a par- 
ticular spot in the chromosome. 

It must be apparent that the hereditary 
characters of an individual animal or plant are 
determined at the time of fertilization of the egg 
from which it comes. If this be so, the common 
belief that prenatal influences produce heritable 
characters must evidently be false. Farmers 


82 THE THIRD AND FOURTH GENERATION 


used to hang a red blanket in the stall of a cow, 
some weeks before a calf was expected, as a 
measure to insure a solid red color in the off- 
spring, as that was very desirable in certain 
breeds. Such a performance is quite useless. 
Jacob believed in accordance with the prevalent 
notion of his day that he increased the number 
of streaked and spotted cattle by a similar pro- 
cess, but the facts related (see Gen., chap. 30) 
are quite as well explicable on the assump- 
tion that Laban’s herds and flocks were hybrid 
stock. Birthmarks are sometimes thought to 
result from something the mother sees or longs 
for during the prenatal life of the child. 
Undoubtedly they are not so produced, and the 
resemblance of a birthmark to some object seen 
or desired is all a matter of chance. Hundreds 
of mothers go through similar experiences 
without the child exhibiting any birthmark. 
Indeed it is quite impossible to conceive how 
any effect could be produced on the develop- 
ing child, for there is no nerve connection 
and no direct blood flow between mother and 
baby. 


THE VISIBLE BASIS OF HEREDITY 83 


It is very evident in the foregoing diagram 
that any two chromosomes other than 6 and o 
might have found their way to the individual 
from the grandparents. What combination 
of chromosomes will finally arrive in any 
individual is a matter of chance. Remember 
that there are forty-eight chromosomes in the 
human cells of the white woman (forty-seven 
in the man), and it is apparent that almost an 
endless number of combinations are possible. 
Half of them in any child come from the mother, 
half from the father, but which ones of the 
forty-eight of the mother will make up the 
twenty-four that go to the child, or which of 
the father’s will be contributed as his share, 
chance only determines; so the probability is 
that no two children of a family have the same 
combination of parental chromosomes, unless it 
be identical twins, which come from the separa- 
tion of the fertilized egg at the two-cell stage, 
each cell producing one child. This very pro- 
cess of sexual reproduction seems to be an excel- 
lent means of producing endless variations in 
the offspring. If one had forty-eight dice in a 


84. ‘THE THIRD AND FOURTH GENERATION 


box and were to shake out twenty-four, there 
is little likelihood that in a lifetime he would 
twice shake out the very same twenty-four. 
The plant breeder recognizes this fact and 
propagates his stock by cuttings rather than 
by the sexual process wherever possible. If a 
tree is grown from an apple seed the fruit 
produced is seldom as good as that on the 
original tree, because when the chromosomes 
‘recombine in the sexual process the chances are 
that so efficient a combination will not again 
arise. So the grower takes a twig from his tree 
and plants it so as to get a new tree whose cells 
possess the same chromosome content as the 
original. It is only in the sexual process that 
reduction and recombination of chromosomes 
occur, and these are the basis of hereditary 
characters. When, however, he is after new 
things, better types of fruits or grains, then the 
breeder not only makes the plants reproduce 
sexually, but he uses as parent forms plants that 
have unlike but desirable characteristics, in the 
hope that some new combination may result 
that will be better than either of the parents. 


THE VISIBLE BASIS OF HEREDITY 85 


QUESTIONS 


1. Have you seen cells under the microscope? You 
can see them with the naked eye in some vegetable 
tissues, when they are much swollen with sap, as in the 
pulp of watermelon, or in the coarse tissue of the 
water-lily leaf or elder pith. Will some member of 
the class supply some such material? Such cells have 
largely lost their living protoplasm. 

2. In cell division what is the customary behavior 
of the chromosomes ? 

3. Why is a reduction in the number of chromo- 
somes necessary when the plant or animal reproduces 
by eggs ? 

4. What primarily determines the sex of an 
animal ? 

5. What is the evidence against birthmarks ? 

6. Why does the fruit-grower propagate by cuttings 
rather than by seed ? 


CHAPTER VII 
SOME APPARENT EXCEPTIONS 


Many of the cases of inheritance that at 
first appeared to be exceptions to Mendel’s 
law are found to be explicable by it, and really 
strengthen our belief in its accuracy and univer- 
sality. Thus several years ago Bateson, one 
of the foremost English investigators, crossed 
two sweet pea plants that bore white blossoms. 
Strangely enough, the offspring were plants that 
had purple blossoms. The plants reared from 
the seed of these purple-flowered kinds were 
part purple, part white, in the proportion of 
9g to 7. Bateson recognized in this the familiar 
Mendelian ratio of 9-3-3-1, though the last 
three terms have united to produce the 7. 
The normal Mendelian ratio indicates that at 
least two factors are involved, and Bateson 
conceived that the purple character is really 
dependent upon two factors, and that both 
must be present to produce it. One of the 

86 


SOME APPARENT EXCEPTIONS 87 


parent white peas evidently contained one 
factor, the other white parent had the other 
factor in it, and when the two came together 
the resulting pea plants produced purple blos- 
soms. Of the offspring of the purple blossom 
peas g contain both factors and are therefore 
purple, 3 contain one factor, 3 the other, 
r neither, and all these are white. 

The original wild sweet pea is purple- 
flowered. The factors for purple have, in the 
course of cultivation, been separated. The 
white peas in the experiment each contain one, 
hence the original purple reappears, a phe- 
nomenon known as reversion—the reappear- 
ance of primitive ancestral traits in the 
offspring of more highly developed animals 
or plants. Many colts exhibit when very 
young more or less of the zebra-like striping 
characteristic of the original horse. Human 
beings are sometimes born with a harelip or 
a clubfoot, conditions that are permanent 
in the lower monkey-like types of mammals; 
it is easier to bite with the front téeth 
when the lips can be drawn out of the way, 


88 ‘THE THIRD AND FouRTH GENERATION 


and turned-in soles of the feet facilitate 
climbing. | 

So many cases similar to that of the peas 
mentioned above have been found that it is 
now recognized as unusual to find a character 
dependent on only one factor. So the factorial 
hypothesis has come into vogue: this means 
that characters as such are not heritable things 
but that there are certain factors that are really 
the heritable units and their interplay causes 
the appearance of a particular character. The 
manifest character in the case given is the 
purple color of the blossom. What the factors 
really are we do not know, but we do believe 
they are heritable units and that together 
they produce the visible color. Occasionally 
one factor may be the sole cause of the 
character; then, of course, the latter acts as 
the heritable unit. Usually a character is 
the resultant of the interplay of several fac- 
tors. Sometimes one factor is instrumental 
in determining several characters. At times 
two or more factors may independently pro- 
duce like results. Some concrete illustrations 


SoME APPARENT EXCEPTIONS 89 


of these several possibilities will make them 
clearer. 

When several factors enter into the pro- 
duction of one character, the phenomena of its 
inheritance are often apparently very compli- 
cated. Thus coat color in rabbits is due to the 
interaction of seven separable factors, three of 
which have to do with the production of color, 
three with its distribution, and one with its 
intensity. Possibly the factors are chemical 
substances whose reactions produce the appar- 
ent effects on the coat color. That is mere 
hypothesis; since we cannot tell just what they 
are, they are designated by letters. The color 
factor, C, must be present to have any color at 
all. If absent, the rabbit is white, an albino. 
B is the factor which acts on C to produce 
black, Y, a factor which acts on C to produce 
yellow. The yellow is obscured by the black 
which overlays it if the factor B is present. E 
is an extension factor, acting on black pigment 
to spread it over the entire body. If this factor 
is absent, only the eyes and the skin of the feet 
are pigmented. U is called the uniformity 


90 THE THIRD AND FOURTH GENERATION 


factor, which if present determines that the 
color shall be uniformly spread over the 
surface. If U is absent the color appears in 
blotches, separated by white areas. A desig- 
nates the agouti factor. When this factor is 
present the color is distributed in a particular 
way in each hair: the tip is black, then follows 
a band of yellow, and the base of the hair is gray. 
The general effect produced is a uniformly gray 
coat color. I stands for the intensity factor, 
which if present makes the black or yellow 
strong. If absent, the black is a diluted black 
or blue, and the yellow becomes cream. If 
factors A, B, C, E, U, are present in the cells of 
an individual, it is a gray, for the agouti hair 
pattern can develop if C is present with factor B 
to operate on it. E determines that the color 
is distributed all over the body, and U that it is 
uniform, not interrupted by white patches. 
But an individual whose cells contain A, B, Y, 
C, E, U, would also be gray, as would one whose 
cells contamn-A).B + Gy HU oreAs: BOCs Gear 
U, I. Some or all of these factors maybe 
present in double dose, so that AA, B, C, E, U; 


SOME APPARENT EXCEPTIONS QI 


AA, BB, C, E, U, etc., are all formulae for the 
factors present in gray rabbits. In fact, there 
may be thirty-two all-over gray rabbits that 
differ in the complex of factors present in their 
body cells. They appear similar, and are 
therefore said to be phenotypically alike; but 
they all may give unlike progeny, since their 
germ cells, eggs and sperm, will contain unlike 
assortments of factors, and they are therefore 
called genotypically unlike. 

If we are crossing two individuals that differ 
in one factor (or one character, if that character 
is determined by a single factor), the ratio of 
individuals in the F, generations is 3 to 1, in 
which 3 possess the factor in question, one does 
not. Of the three, one has it in double dose, 
two in single dose. There are two phenotypes 
in this case, ie., two differently appearing 
animals or plants, and three genotypes. If two 
factors are involved, the proportion is 9-3-3-1, 
that is (3-+1)?. A reference to the checker- 
board (p. 43) showing possible combinations 
in the F’ generation in this case shows there are 
four phenotypes (2?) and nine genotypes (37). 


92 THE THIRD AND FOURTH GENERATION 


In ‘the same way when two individuals are 
crossed differing in three factors, the proportion 
in the F, generation is 27-9-9-9-3-3-3-1(3-+1)5, 
and there are eight phenotypes (23) and 
twenty-seven genotypes (33). When seven fac- 
tors are involved, the proportion obtaining in 
the different sorts of offspring in the F, genera- 
tion is (3-++1)’, and there are 128 phenotypes (27) 
and 2,187 genotypes (37). So that if one were 
to mate the albino rabbit with the factors BB, 
EE, UU, II, AA, in its cells (no factor C is 
present, so it is colorless) with the cream 
mottled white whose cells have YY, CC, the 
offspring will be gray. If these grays are 
mated, 128 different sorts of rabbits, as far as 
appearances go, might appear in the offspring, 
and there would be possible more than 2,000 
combinations of factors in their cells. ‘This 
illustration makes apparent the almost limitless 
complexities involved in tracing the inheritance 
of any character dependent on the interplay of 
several factors. 

The following case will illustrate the presence 
of two factors, either of which may cause the 


SOME APPARENT EXCEPTIONS 93 


character. It was found at the Swedish Experi- 
ment Station at Sval6v, previously mentioned, 
that when two wheat plants were crossed, one 
of which had kernels that were brown coated, 
the other white coated, the expected Mendelian 
ratio of 3 to 1 in the F, generation did not 
appear, but the brown-coated kernels were 
fifteen times as numerous as the white-coated, 
and were of several shades of brown. The 
ratio 15 to 1 evidently suggests that two factors 
are involved, but the customary grouping 
9-3-3-1 is changed, so that the first three terms 
are united in a single term. Nilsson, Director 
of the Swedish Station, supposes that there are 
two factors present, either of which produces 
brown (see checkerboard). Both are present in 
double dose in the offspring in the F,, generation, 
in one case out of the 16, and the brown color is 
very deep. One is present in double dose, the 
other in single dose in 4 cases, and the brown 
color is less pronounced. Only one is present 
either in double dose or single dose in 6 cases, 
and the brown color is still paler. Neither is 
present in one case, the white. In another 


94 ‘THE THIRD AND FouRTH GENERATION 


wheat the coat color is red. When crossed with 
the white-coated wheat the proportion of F, 
offspring is 62 red of varied shades and 1 
white. Evidently there are three factors 























Eggs 
on Bb B b 
Sperm 
Bb BBbb BBb Bbb Bb 
B BBb BB Bb B 
b Bbb Bb bb b 
Bb B b 





producing red in this case, and the possible 
shades of red are very numerous in this F, 
generation. 

Davenport believes that his study of crosses 
between whites and negroes shows with a fair 
degree of probability that the full-blooded 
African negro has two factors for black in his 


SOME APPARENT EXCEPTIONS 95 


skin, besides factors for red and yellow. The 
white individual has the same pigments present 
in the skin but in different proportions. The 
skin of a tanned brunette appears on micro- 
scopic examination identical with that of the 
negro. ‘There are of course other distinctive 
negro features, like the crinkly hair and broad 
nose. The two black factors may be designated 
A and B, and they are present in double dose, 
so that the chromosomes of a negro would 
contain AA, BB. The germ cells after reduc- 
tion must then contain factors A and B. The 
mulatto (cross of the black and white) would 
have the same two factors in the body cells 
both brought in at fertilization by the negro 
sex cell, while the corresponding white sex cell 
would contain neither factor. Egg or sperm of 
a mulatto may therefore conceivably contain 
A. and 5B, A,. B, or neither. The possible 
resulting combinations when the egg is ferti- 
lized by a sperm are (construct the checker- 
board) 1 AA BB, a full-blooded negro; 2 AA 
T5 ere GAS IS Ls eee ely ae Ta LN ele 1 1 ed A 2B 
and one neither A nor B, the latter a pure white. 


96 ‘THE THIRD AND FouRTH GENERATION 


The several combinations in this list between 
that of the full-blooded negro and the pure white 
make ‘possible several shades of dark pigmenta- 
tion. What appears as a blend of black and 
white resulting in a dilute black is really the 
inheritance of one or more of these black 
determiners, thus producing the several possible 
intermediate shades. 

Little is known as yet concerning the 
behavior of the other negro characteristics in 
inheritance. They apparently are largely inde- 
pendent of each other and of skin color, so that 
in crosses with whites the broad nose, the thick 
lips, or the long arms may any or all appear 
in a very light individual, while a dark-skinned 
individual may have the features of the white. 
Negro blood is not necessarily an index of 
mental inferiority. W. E. Burghardt DuBois, 
author, professor of economics at Atlanta 
University, an acknowledged leader in southern 
problems, and Paul Laurence Dunbar, American 
poet, are samples of the continually recurrent 
intellectual ability in individuals of pure negro 
extraction. 


SoME APPARENT EXCEPTIONS 07 


Another apparent exception to Mendel’s 
law is the inheritance of sex-linked characters, 
but it also is explicable on the supposition that 
the factor or factors that determine the char- 
acter are contained in the sex chromosome. 
In fruit flies, reared in Professor Morgan’s 
laboratory, there appeared a sport with white 
eyes.: The normal fly has red eyes. The 
factor for red in the eye, it is supposed, is 
carried by the sex chromosome. We may 
represent the sex chromosome by ® and show 
the presence of the red factor by making it 
black, its absence by leaving it uncolored, ©. 
Since the female has a double dose of the sex 
chromosome, the male a single dose, a cross 
of the red-eyed male and the white-eyed female 
would be represented thus: 


White-eyed female @9 [e] Red-eyed male 
Eggs all alike O Sperm of two sorts 
© pe sor 


The offspring in the F, generation would be of 
two sorts, [0]; the left-hand diagram repre- 
senting the red-eyed females, the right-hand 
the white-eyed males. There will be equal 


98 THE THIRD AND FOURTH GENERATION 


numbers of each, since the chances are equal 
that the egg will be fertilized by either sort 
of sperm. ‘The expected Mendelian phenom- 
enon does not appear, for we should anticipate 
that in crossing a red-eyed with a white-eyed, 
the F, generation would be all either red or 
white, depending on which character is domi- 
nant. But if we make the supposition sug- 
gested, viz., that the factor for red eye is 
carried by the sex chromosome, the facts found 
are adequately explained by the hypothesis, and 
this does no violence to Mendel’s law. It is 
merely an extension of it. 

There is one form of color blindness in human 
beings that is customarily confined to men. 
Still, the daughter of such a color-blind father, 
though herself normal, may transmit the 
difficulty to some of her sons. If we suppose 
that the factor for the perception of color is 
carried in a sex chromosome, color-blind men 
would be represented thus, [0]; and the normal 
female so, @@. The eggs from the female will 
be all of one type, ©; the sperm from the 
male of two sorts, one with the sex chromo- 


SOME APPARENT EXCEPTIONS 99 


some, which, however, does not carry the factor 
for perception of color, —, the other without 
the sex chromosome. The egg may be fertilized 
by either of these two types of sperm, and the 
results will be either, first, females that perceive 
color, @d; or, secondly, males that perceive 
color, {e]. The color blindness seems to skip 
this generation. If now this woman mates 
with a normal man, the eggs may be of two 
sorts, those containing the sex chromosome 
that carries the factor for the perception of 
color, ®; or those with the sex chromosome 
that does not carry the factor for perception of 
color, ©. The sperm from the normal father 
will be of two sorts, those that carry the sex 
chromosome containing the factor for per- 
ception of color, and those that have no sex 
chromosome. Either sort of egg may be ferti- 
lized by either sort of sperm, so that we may 
get in the next generation, first, normal 
daughters, @e; secondly, daughters like their 
mother, @0); and color-blind males, [o]. In the 
same way it is evident that if a woman like 
the one just considered were to mate with the 


1oo)6'6THE THIRD AND FOURTH GENERATION 


color-blind man, there would result, not only 
normal and color-blind sons, but also color- 
blind daughters. 


QUESTIONS 


t. Will you state Bateson’s experiment to show 
clearly that a particular character may be due to the 
interaction of several heritable factors? Can someone 
give an experience in breeding rabbits or corn that 
illustrates the factorial hypothesis ? 

2. How will you explain the various shades of color 
that result from the crossing of whites and negroes ? 

3. What is meant by a sex-linked character ? 

4. Can you explain the peculiar transmission of 
color blindness through a female who is herself not 
color-blind ? 


CHAP THRAV LLL 


ARE ACQUIRED MODIFICATIONS 
HERITABLE ? 

One of the very live questions in heredity at 
the present time is whether or not acquired 
modifications can be transmitted from parents 
to offspring. The term ‘acquired modifica- 
tion” or “acquired character” is used with a 
very definite meaning in all discussions of 
heredity. In one sense all new characters are 
acquired. If we believe in the derivation of 
the more complex animals and plants from 
relatively simple types (the doctrine of evolu- 
tion), evidently the characters which later 
animals come to possess are not possessed by 
the earlier forms from which they are derived. 
Thus in the early rock strata we find no verte- 
brate animals; later the vertebrates appeared. 
The vertebrate character is one, therefore, that 
was acquired by the animals in due course of 
time. It is not, in this sense, however, that 


ror 


102 THE THIRD AND FouURTH GENERATION 


the biologist uses the term “acquired char- 


9) 


acter.”” By “acquired character,” or better— 
‘acquired modification,” is meant some feature 
which the animal or plant body takes on 
directly in response to the changing environ- 
ment, and it is a question whether such acquired 
modifications are transmissible. 

The older naturalists took this for granted. 
Thus we find that if certain plants which 
ordinarily grow in the lowlands are _ trans- 
planted to an Alpine environment, high up on 
the mountain, they become dwarfed, frequently 
acquire a high degree of hairiness, and not 
uncommonly the blossoms increase in brilliancy. 
The progeny of such plants manifest the same 
modifications, and it was taken for granted 
that they transmit such to their offspring. 

Our field corn was originally a tropical plant. 
The varieties that one finds now in the southern 
states require a long season for maturation. As 
the corn plant was introduced gradually farther 
and farther north it began to ripen its seed more 
rapidly, until we find such northern varieties 


as Peep 0’ Day, produced by the northern seed- 


ACQUIRED MODIFICATIONS HERITABLE? 103 


houses, come to maturity in the short summer 
of these extremely northern states. It looks 
very much as if the short season had had a 
direct effect upon the corn, and the remarkable 
thing is that such breeds of corn, when taken 
south again, retain their habit of early ripening 
more or less completely, as also do their off- 
spring. On the face of it, it appears as if this 
were an example of the acquisition of a new 
character as a result of environmental influ- 
ences, and that this acquired modification was 
transmitted to the progeny. When, however, 
we examine this case more carefully, it is very 
evident that other interpretations are possible. 
In any field of corn there will be found some 
plants that ripen earlier than others. In other 
words, there is a degree of variability present 
in this as in other characters. Evidently, as 
corn is planted farther and farther north, only | 
the seed from plants that mature early can be 
gathered for planting next year. The late 
maturing plant would be nipped by the frost 
and killed, and would leave no seed. One 


would, therefore, continually get a selection of 


104 THE THIRD AND FOURTH GENERATION 


strains that ripen at earlier and earlier times, 
and the resultant very early ripening variety 
would come about by the elimination of all 
those plants that did not have in their germ 
cells the early ripening trait. 

All through the Central West we have one 
species of chipmunk. In the Rocky Mountain 
region, however, we have a great many dif- 
ferent species. Wherever there is an isolated 
valley, hemmed in by impassable mountain 
barriers, there you are very prone to find a 
species peculiar to that valley. It looks as if, 
when the mountains were upheaving, some of 
the chipmunks that originally roamed the 
entire region were isolated, and had gradually 
changed their character as the environmental 
influences of this particular locality had time 
to operate upon them. Now these new species 
breed true, and again it looks as if we had the 
transmission of an acquired modification. But 
we may interpret the phenomenon in a different 
way. Itmay be that the hereditary germ mate- 
rial is subject to wide variation, and that only 
those varieties have survived whose germinal 


ACQUIRED MODIFICATIONS HERITABLE? 105 


variations adapted them to the particular style 
of environment. 

Since it seems impossible to settle this 
doubtful point by observations in the field, the 
biologist has had recourse to experiment. 
There are a number of experiments that have 
been unconsciously conducted by the race 
for generations. Chinese women, from time 
immemorial, have had their feet bound when 
they were very little girls so as to _ pro- 
duce the deformed, but stylish, foot. Here. 
is a modification which has been impressed 
on the body of the Chinese women repeatedly, 
and yet Chinese babies are born with as 
perfect feet as any other babies. It is stylish, 
among the Flathead Indians, to possess a 
forehead that slopes back from just over the 
eyes to a peak at the top of the head. 
To produce this feature, a board is bound on 
the head of the growing Flathead Indian 
baby. In spite of the fact that this cus- 
tom has obtained for many centuries, the 
babies persist in coming into the world with 
perfectly normal heads. 


106 THE THIRD AND FourRTH GENERATION 


The most noted experiment that seems to 
give support to the notion that acquired 
modifications are inherited is the experiment of 
Brown-Sequard with guinea-pigs. Brown- 
Sequard so injured the nervous system of adult 
guinea-pigs that they had frequent epileptic 
seizures. It was found that the offspring of 
these animals also had much more frequent 
attacks of epilepsy than the offspring of normal 
pigs. But this experiment lacks confirmation. 
It has been tried by later experimenters without 
achieving the results that Brown-Sequard 
claims. 

The first serious doubt of the inheritance of 
acquired characters was raised by Weismann 
in the latter part of the last century. Weis- 
mann, in his study of some of the lower animals, 
was struck by the fact that those cells in the 
animal body which ultimately give rise to the 
eggs or the sperm seem to have a history that 
is more or less disconnected from and inde- 
pendent of the rest of the organism. We have 
already seen that any animal or plant originates 
from one single cell; that by repeated divisions 


ACQUIRED MODIFICATIONS HERITABLE? 107 


this cell (fertilized egg) gives rise to the rest 
of the cells that make up the animal or plant. 
Most of these cells differentiate as they assume 
different functions. ‘Thus in the animal we 
have muscle cells, nerve cells, gland cells, and 
corresponding differentiations in the tissues of 
plants. But those cells that are going to give 
rise to the eggs and sperm are relatively undif- 
ferentiated, maintaining more or less completely 
their embryonic character. To these cells 
Weismann gave the name of germ cells, to 
distinguish them from the cells which go to 
make up the rest of the body, which he called 
the somatic cells. The protoplasm of the germ 
cells he designates germ plasm, that of the 
somatic cells, soma plasm, and Weismann’s 
contention is that the germ plasm is continuous 
generation after generation. It is the germ 
plasm that gives rise to the soma plasm, not the 
reverse, or, to put it in more concrete form, it is 
the egg which gives rise to the chick, and to the 
eggs which its body contains, rather than the 
chick which gives rise to the egg. The dia- 
gram (Fig. 7) will make this plainer. The 


108 THE THIRD AND FOURTH GENERATION 


cells which separate from the germinal material 
differentiate into the body of the chicken, while 
the undifferentiated germ cells continue and 





Fic. 7.—At the left the old idea is illustrated that the chicken 
gives rise to an egg from which comes another chicken that pro- 
duces an egg, etc. At the right the modern conception is shown: 
the egg gives rise to more egg-forming material and also to the 
body of the chicken. The germ plasm is thus continuous. 


furnish the eggs out of which the next genera- 
tion of chickens will develop. It is a mere 
coincidence that the germ cells are contained 
within the body of the parent. If this is true, 
it is evidently difficult to conceive how changes 


ACQUIRED MODIFICATIONS HERITABLE? 109 


which affect only the body of the chicken can 
influence later chickens, because the only 
direct connection between the chick and its 
offspring is back through an egg which goes 
out of existence as it develops into the chick 
and more of the germ plasm. 

In several animals we have evidence of this 
early separation of the soma plasm from the 
germ plasm. Even in the four-cell stage of the 
developing egg of Ascaris, a round worm com- 
mon in the intestine of the horse and hog, the 
body cells are marked off from the germ cells 
by the fact that certain portions of the chromo- 
somes disappear in the body cells, while they 
remain in the germ cell. Thus only one cell of 
the four continues as germ material, while the 
other three give rise to the body cells. Simi- 
larly, in Miaster, one of the flies, the somatic 
cells are clearly distinguished from the germ 
cells by the eight-cell stage of the developing 
egg. And in many other animals we can. trace 
this separation back to an early stage in develop- 
ment. We seem to have, then, fairly positive 
evidence that Weismann’s contention is correct, 


110 6oTHE THIRD AND FOURTH GENERATION 


and that there is a continuous stream of germ 
plasm going from parent to offspring, generation 
after generation, and that this is more or less 
independent of the body plasm. It is then easy 
to see why offspring are like their parents; 
both are produced from the same stuff, the 
germ plasm. 

To see whether or no the body plasm would 
affect the germ plasm contained in it, this 
experiment was tried. The ovaries of a black 
guinea-pig were transplanted to a white pig 
after the ovaries of the latter animal had been 
removed. When the wounds had healed, and 
the animal had recovered perfectly, this white 
female with ovaries from a black was mated toa 
white male. Now we know that the offspring 
should be all white animals, under normal 
conditions, when two whites are thus mated. 
If the white female had affected the germ plasm 
in the transplanted ovaries, something of the 
same result would be achieved. As a matter of 
fact, all the young born were black, with no 
intimation of white, which is the result that 
would follow from mating a black female to 


ACQUIRED MODIFICATIONS HERITABLE? III 


a white male, since black is the dominant 
character. Of course experiments of this type 
must be multiplied before we reach a certain 
conclusion, but, as far as the evidence goes, it 
looks as if the body plasm were early set off 
from the body germ, and that the former had 
little or no effect upon the germ plasm. 

Such a conclusion is also compatible with the 
results achieved in the experiments cited before, 
viz., that acquired characters, which are modi- 
fications that impress the body plasm only, can- 
not be transmitted. To put this result in more 
concrete manner it would mean this: that if a 
person in whose ancestry tuberculosis had 
seldom or never occurred should come down 
with the disease and ultimately die of it, 
children of such an individual would be no more 
prone to the disease as far as inheritance is 
concerned than the children of a person who 
has not died of tuberculosis. Conversely, this 
would be true: that if a person in whose ances- 
try tuberculosis was a very common cause of 
death should, by hygienic living and wise pre- 
cautions, avoid tuberculosis, the hereditary 


112 THe THIRD AND FouURTH GENERATION 


tendency to the disease would yet be trans- 
mitted quite as forcefully to the children. 
This illustration is based on the conception that 
the tendency to tuberculosis is a distinctly 
heritable thing. That is not yet conclusively 
proven, though it is probable. The non- 
inheritance of acquired characters would mean 
that the man who has laboriously achieved an 
education does not thereby make it easier as 
far as hereditary influences are concerned for 
his children to achieve an education. They 
must start at the same point as the parent. 
The expression “‘in so far as hereditary 
influences are concerned”’ is repeatedly used 
because undoubtedly the child of the tubercular 
parent is handicapped by living in an atmos- 
phere more or less overcharged with tubercular 
germs, and the child in the cultured home of the 
educated individual has the advantage of the 
inspiring and stimulating contact with people of — 
distinct mental ability. We must clearly dis- 
tinguish, in other words, between physical 
inheritance and social inheritance. Each gen- 
eration passes on to the next a mass of social 


ACQUIRED MODIFICATIONS HERITABLE? 113 


institutions, culture, and ideals that have 
gradually been developed at the expense of 
much effort, so that the child of today finds 
himself growing up in an environment that 
makes success along many lines infinitely easier 
than for a child of several generations ago. 
This transmission from generation to generation 
of the body of social customs and achievements 
may be termed social heredity, but evidently 
it is quite distinct from the thing which we 
ordinarily speak of as heredity—the physi- 
cal transmission of characters from parent to 
offspring. 

While it is generally accepted that no envi- 
ronmental influence can affect the body in such 
a way as to be transmitted, the environmental 
influence may directly affect the germ cells. 
Tower found in experiments on potato beetles 
that it was possible to produce exceptionally 
dark animals if the young were reared from the 
egg in very moist air that was unusually warm, 
and that, conversely, the animals were very 
pale if reared in dry cold air. The potato 
beetle is peculiar in that the germ cells lie 


114 THE THIRD AND FouRTH GENERATION 


dormant through most of the life-history of the 
animal, growing rapidly to produce the eggs 
and sperm during a very short period when the 
animal is quite mature. If, now, the beetles 
are kept under the conditions of excessive 
moisture and high temperature while these 
germ cells are undergoing rapid multiplication, 
no effect 1s produced on the beetles themselves, 
for they are already mature, but their offspring 
are exceptionally dark in successive generations. 
On the contrary, the young reared under these 
same conditions, but removed before the sex 
cells go through their period of rapid develop- 
ment, are themselves dark, but their young 
show no effect of the altered conditions, being 
normally colored. It is very evident that in 
the last case we have affected only the grow- 
ing body; in the former case only the germ 
cells. 

Stockard has made some very interesting 
experiments with guinea-pigs. By putting 
guinea-pigs into a cage, the air of which was 
more or less saturated with the vapor of 
alcohol, he could habituate the pigs to the use 


ACQUIRED MODIFICATIONS HERITABLE? II5 


of alcohol. Numerous pairs of guinea-pigs were 
subjected to the alcohol, some for brief periods, 
others for long periods. At the same time 
other pairs of guinea-pigs from the same litters 
were kept under normal conditions. It was 
found that the guinea-pigs that were more or 
less confirmed drunkards gave birth to a larger 
number of young than normal pigs, but a high 
proportion of these young were born dead. A 
much higher percentage of them died in early 
life than did the offspring of the normal pigs, 
a great many of them were born deformed, and 
many were prone to serious nervous diseases, 
such as epileptic seizures. Furthermore, it was 
found that such results followed more commonly 
when the father was an inebriate than when 
the mother was addicted to alcohol, if parents 
were used one of whom was exposed to the 
influence of the alcohol and the other was 
normal. Another interesting result followed 
from the matings of the offspring of inebriate 
parents when the young so mated were not 
themselves habituated to the alcohol. The 
young produced showed the deleterious effects 


116 ‘THE THIRD AND FourTH GENERATION 


already mentioned even more than the offspring 
of alcoholized parents. In other words, the 
grandchildren suffered more than the children 
from the debauches of their ancestors. The 
only conclusion that we care to draw at present 
is that germ cells evidently may be directly 
affected by factors in the environment. 
Experiments on other animals made in the 
same way as Stockard’s experiments indicate 
that the results achieved by Stockard do not 
necessarily obtain in all their details. White 
rats were tested as follows to determine the 
rate at which they learned. They were first 
accustomed to feed at one corner of their cage. 
Then partitions were set in so that the food 
was out of sight at the end of a maze of pas- 
sages. Each rat was tested separately and at 
first wandered about in a tortuous course in its 
attempt to find the customary food. In the 
course of repeated trials day after day it learned 
to omit some of the unnecessary windings and 
finally went directly to the food. The length 
of time it took a rat to learn its way unerringly 
along the passages to the food was an index of 


ACQUIRED MODIFICATIONS HERITABLE? 117 


its educability. It was found that the off- 
spring of rats accustomed to habits of inebriety 
learned more readily than those of non- 
alcoholized rats. Hodge found the reverse to 
be true for dogs. 

So far as the statistics of human inebriety 
go, it appears that the children of moderate and 
even of excessive drinkers are not inferior to 
the general run of children from the same social 
stratum. It is true, however, that there is a 
high percentage of defective offspring from 
parents who are addicted to alcoholic debauches. 
These apparently contradictory findings are 
harmonized in this way. Alcoholism is a 
symptom rather than a cause. It denotes 
nervous degeneracy. The children from such 
defective germ plasm are very prone to mani- 
fest nervous defects, such as alcoholic mania, 
insanity, epileptic seizures, imbecility, and so 
on. This topic will be further discussed in 
the next chapter. It is touched upon here to 
make clear this point, that while acquired 
modifications are not transmissible hereditarily, 
those influences which affect the body may 


118 THE THIRD AND FourtH GENERATION 


also directly affect the germ plasm and produce 
heritable results. 

There is one set of diseases which, while they 
are not heritable in the sense that they are 
transmitted through the germ plasm, are yet 
directly passed from the parent to the offspring. 
These are some of the venereal diseases, such 
as syphilis and gonorrhea. They are no more 
heritable than smallpox or scarlet fever, but 
since they are diseases of the sex organs, and 
the child in the process of being born must come 
in contact with these sex organs, the child is 
practically certain to catch the disease from its 
parent. ‘They are exceedingly persistent and 
readily infectious. While they are commonly 
passed from individual to individual by the 
intercourse of the sexes, a perfectly innocent 
person may get the contagion by using an 
unclean toilet or merely by personal contact, 
touching or kissing an individual who is 
seriously affected with the disease. Gonorrhea 
is responsible for a very large percentage 
(probably 80 per cent) of the blindness of 
infants and for a large percentage of the opera- 


ACQUIRED MODIFICATIONS HERITABLE? 119 


tions involving the abdominal organs of women. 
Syphilis is responsible for more or less of feeble- 
mindedness and for much insanity, and it prob- 
ably is the direct cause of locomotor ataxia, of 
softening of the brain, and a frequent contribut- 
ing cause to hardening of the arteries and death 
from the rupture of brain blood vessels. 

It is probably safe to say that these diseases 
are the cause of more misery than all of the 
other diseases put together. It is difficult to 
make a cautious statement of their results. 
Even conservative physicians in writing of their 
effects are prone to make assertions that read 
like those of the alarmist. They are undoubt- 
edly spread chiefly by sexual impurity. So 
appalling are their results that many extreme 
measures have been advocated to check their 
havoc. Some states now prescribe that before 
a marriage can be legally performed both the 
contracting parties must furnish to the proper 
authorities a certificate that they are free from 
venereal diseases. Some states, recognizing the 
correlation between these diseases and crime, 
insanity, imbecility, and pauperism, provide 


120 ‘THE THIRD AND FourTtTH GENERATION 


for the segregation of such people and their 
confinement under conditions which will make 
the bearing of children impossible. In some 
states it is incumbent upon the authorities in 
charge of persons in insane asylums, peni- 
tentiaries, and institutions for the feeble-minded 
to sterilize such as are adjudged to be hopeless 
cases. But probably the most effective method 
of dealing with the situation is to bring to young 
people a realization of the prevalence of such 
diseases, even among men of the better social 
classes. 

These diseases are curable, but only after 
prolonged treatment, and then only in a small 
percentage of the cases treated. The effects of 
such sins as alcoholism and sexual impurity are 
transmitted apparently to the children to the 
third and fourth generation. In the case of the 
latter disease, at least, the transmission is not 
the truly hereditary transmission, but the evil 
effects are just as serious as if it were true 
inheritance. It is to be noted that the effects 
of these conditions seldom do run for many 
generations. The stock is very prone to die 


ACQUIRED MODIFICATIONS HERITABLE? 121 


out. The striking biblical passage seems sig- 
nificantly true in this connection. 


QUESTIONS 


1. Can you give examples of acquired modifications 
not mentioned in the book ? 

2. Will you give some examples of the apparent 
transmission of acquired modifications that are other- 
wise explicable ? 

3. Recall Tower’s experiments with potato beetles, 
and then make clear the distinction between the influ- 
ence of an environmental factor upon the body plasm 
and upon the germ plasm. 

4. What is the evidence that it is possible for alcohol 
to directly injure the germ cells and so produce deteri- 
- oration in the offspring ? 

5. In what way is it possible for the “sins of the 
fathers”’ to be visited upon the “‘children to the third 
and fourth generation”’ ? 


CHAPTER IX 


THE INHERITANCE OF HUMAN CHARAC- 
TERS, PHYSICAL AND MENTAL 

Anyone who undertakes to trace the ances- 
try of an individual is soon impressed with the 
fact that it is a difficult task even to find the 
names of the persons involved three or four 
generations back; it is much more difficult to 
determine with certainty their physical and 
mental characteristics. One can more surely 
find the pedigree of a horse or hog that he may 
own than he can of a child in whom he is 
interested, for we do have registry books for 
good stock, but none ordinarily for human 
family relations (in Illinois not even compul- 
sory birth registrations until very recently), so 
that a child born in this state may not even 
legally prove his existence or parentage by 
official records. It is not an easy matter, 
therefore, to find human data that illustrate 
the various phases of heredity concerning 


I22 


INHERITANCE OF HUMAN CHARACTERS 123 


which we are reasonably sure in dealing with 
animals and plants. 

Fortunately, there are some studies of the 
inheritance of physical characters that are 
quite satisfactory. There is an increasing 
number of studies of the inheritance of insanity, 
feeble-mindedness, epilepsy, and alcoholism by 
the scientific staff of institutions dealing with 
such cases, and we do have a fairly good mass 
of material in the lines of descent of the royal 
families of Europe, where the matings and the 
characters of the individuals are more or less 
matters of history. Thanks to the generosity 
of some men of wealth and foresight, apprecia- 
tive of the importance of a better knowledge 
of the laws of human heredity, we have in 
several countries well-endowed laboratories 
with expert staffs founded on purpose to study 
this topic; such are the Galton Laboratory of 
Eugenics in England and the Eugenics Labora- 
tory of the Carnegie Institution, Cold Springs 
Harbor, New York. 

Occasionally a family is found in which one 
or more members have five fingers instead of 


124 THE THIRD AND FouRTH GENERATION 


four; such a condition is known as polydactyl- 
ism. Sometimes a case is recorded in which a 
person has fingers with two joints instead of 
three and a thumb with one joint in place of 
two (brachydactylism). Such human abnor- 
malities are inherited. There is given on the 
opposite page a chart (Fig. 8) of a family 
tree in which brachydactylism is very common; 
it is based on a study made by Drinkwater. 
Males in the chart are represented by 4, 
females by 2, matings by =. The circles are 
of solid color @ in individuals affected with the 
deformity, open O in normal individuals. The 
character seems to behave like a Mendelian 
dominant, though one could make no very posi- 
tive assertion on this point from so few indi- 
viduals. But it is very evident that such a 
physical character once in the stock is trans- 
mitted generation after generation, reappearing 
continually in the offspring. } 

There is presented on p. 127 a chart (Fig. 9) 
of the transmission of cataract. This disease is 
characterized by the appearance of an opaque 
area in the usually transparent parts of the 


125 


INHERITANCE OF HUMAN CHARACTERS 


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126 THE THIRD AND FOURTH GENERATION 


eye, ultimately rendering the person blind. 
In the particular form of the disease here con- 
sidered it does not develop until middle life. 
Clarence Loeb in a study of hereditary blindness 
published in 1909 tabulated the results of a 
study of 304 families in which such blindness 
occurs. There were 1,012 children, of whom 
58 per cent were afflicted, which is about the 
percentage expected when hybrid defectives 
mate with normal individuals and the defect 
is a dominant character. Similar extensive 
studies of congenital deafness and deaf-mutism 
show that these are similarly heritable, though 
just how the character behaves is not yet known, 
for undoubtedly under “‘deafness’’ are included 
a variety of diseased conditions that must be 
studied separately before we shall know how 
each is inherited. Care must be taken, too, to 
distinguish between congenital deafness and 
blindness—that which inheres in the germ 
plasm—and those forms, due to accident or 
contagious disease, which are acquired modifica- 
tions and so not heritable. ‘Thus measles often 
produces deafness as one of its after effects. 


INHERITANCE OF HUMAN CHARACTERS 127 


Persons so rendered deaf would not transmit the 
affliction to their children any more than they 
would transmit blindness if the eyes of the 
parents were put out by accident. 


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Fic. 9.—Inheritance of one form of cataract. Modified 
from Nettleship’s chart. The diagram reads thus: A man with 
cataract married a normal woman; of their eight children six 
were affected with the disease. One of these married an un- 
affected man; three of the children of this union were normal, 
sex unrecorded, two defective. This same man married a 
second wife who was normal; their eight children were all un- 
affected. Socontinue reading through five generations. 


Feeble-mindedness apparently behaves as a 
Mendelian recessive. Goddard’s studies of the 
family pedigree of the inmates of the Vineland, 
New Jersey, institution for the care of the 
feeble-minded gives us an abundance of material 


128 THe THIRD AND FOURTH GENERATION 


to show the heritability of this defect and its 
relation to alcoholism, insanity, syphilis, etc. 
Briefly, syphilitic infection is a fairly common 
cause of feeble-mindedness in children. ‘There 
is a higher percentage of feeble-mindedness in 
the offspring of alcoholic parents than among 
those of parents not addicted to it. There 
seems little or no causal relation between 
feeble-mindedness and insanity. But aside 
from feeble-mindedness that may be produced 
by such causes or by occasional accidents such 
as falls, blows on the head, there is the great 
mass of feeble-mindedness that is wholly a 
matter of heredity. 

If a feeble-minded individual comes from 
parents both of whom are congenitally feeble-_ 
minded or who both have a great deal of feeble- 
mindedness in their ancestry, such a one is taken 
to be a pure recessive as far as this character is 
concerned, and his germ cells have a double 
dose of the factor for feeble-mindedness (FF). 
When two such persons mate, their offspring 
would be expected to be all feeble-minded, for 
all eggs and sperm contain the factor F, and 


INHERITANCE OF HUMAN CHARACTERS 129 


when any egg is fertilized the person produced is 
an FF individual. Out of 144 such matings 
resulting in 482 offspring whose records are 
known, Goddard found that 476 were feeble- 
minded. ‘This type of mating as well as others 
cited below are illustrated in the family pedi- 
grees shown on pages 130 and 131, selected 
from Goddard’s book. 

If a person comes from parents one of whom 
is entirely normal and one is feeble-minded with 
many feeble-minded ancestors, it is probable 
that such an individual is a hybrid with germ 
‘cells that, as far as this one character is con- 
cerned, can be designated NF. Such a person 
will pass for normal, since feeble-mindedness is 
recessive. If such a one mates with the type 
described above (FF), it would be expected 
that half the offspring would be normal, half 
feeble-minded. Out of 122 such matings pro- 
ducing 371 children, 193 were found to be 
feeble-minded, 178 normal, which is remarkably 
close to expectation considering the difficulty of 
determining with certainty the real character 
of the parents. When two individuals of the 


130 


THE THIRD AND FourRTH GENERATION 


NF type mate, their offspring would be expected 








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Fic, 10.—Family of Gertie K. 


to give 3 normals to 1 
feeble-minded. Out of 
146 children produced by 
33 such matings Goddard 
found 39 were _ feeble- 
minded. 

The first of Goddard’s 
charts (Fig. 10) 
trates the family tree of 


illus- 


Gertie Skea toinoieng 
years, with the mental 
development of a child ~ 
Males in this. and 
the following chart are 


of 7. 


represented by squares, 
females by circles. Note 
that this girl has a feeble- 


minded brother and that 


both her parents are 
feeble-minded and see the 
appalling array of feeble- 


minded cousins, aunts, uncles, and other rela- 


tives. 


Her grandmother passed for a normal 


INHERITANCE OF HUMAN CHARACTERS 131 


individual, although it would seem from her 
children she must have been an NF individual. 
The second chart (Fig. 11) is quite exactly 


Mendelian, if we suppose the grandparents were 


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CHARLIE M. 


Fic. 11.—Family of Charlie M. (From Goddard’s Feeble 
mindedness.) 


NF individuals. This case is_ particularly 
interesting, for the parents of these six feeble- 
minded children were high-grade morons, both 
immigrants. The public must support the 
children because we have as yet instituted no 


expert examinations to detect such defectives 


132 THE THIRD AND FOURTH GENERATION 


among our immigrants in order to refuse them 
admission to this country. 

See what a single unfortunate alliance can 
produce. A young man to whom Goddard 
gives the fictitious name of Martin Kallikak 
had children by a feeble-minded girl in the days 
before the Civil War. ‘There have been traced 
some 480 descendants from this mating, and all 
of them are below normal intelligence. Later 
this same man married a good Quaker girl, and 
496 of the descendants of this marriage have 
been traced, all of normal mentality. The 
contrast is strikingly instructive, for the con- 
ditions are almost those demanded by a 
scientific demonstration. 

Such cases as those cited are interesting 
from the standpoint of the student of heredity. 
They are tremendously significant to the 
average citizen because there is in the United 
States a very large feeble-minded population, 
estimated at 200,000, nine-tenths of whom are 
at large, free to reproduce their kind, and very 
prone to interbreed, because the feeble-minded 
are seldom sought as legitimate mates by persons 


INHERITANCE OF HUMAN CHARACTERS 133 


of normal mentality. The number of feeble- 
minded is apparently increasing much more 
rapidly than the general population. How 
rapidly, it is impossible to determine, for we 
have no exact data on the number of feeble- 
minded; we are not yet awake to the enormity 
of the problem involved. From these feeble- 
minded come some 40 per cent of our prosti- 
tutes, a fourth of our criminals, and at least a 
half of the inmates of our almshouses. 

A generation ago the valley of Aosta, in 
Northern Italy, was overrun with feeble-minded 
and idiotic individuals of the type known as 
cretins. It was estimated that fully 60 per 
cent of the population were affected with this 
abnormality. A law was passed and enforced 
segregating the really irresponsible cases and 
prohibiting the marriage of cretin with cretin. 
Now the condition has almost disappeared, 
and it is estimated that only a very small 
percentage of the population are cretins, these 
nearly all old, so that this particular form of 
idiocy will there very soon be a thing of the past. 
It seems only a rational procedure to accomplish 


134 THE THIRD AND FOURTH GENERATION 


at least a segregation of feeble-minded in this 
country, even if no more drastic action is taken. 
Otherwise the group is bound to be an increas- 
ing burden on the community, adding con- 
stantly to the tax needed for their support. 
Investigations of competent officials in the 
employ of insane hospitals have accumulated 
a mass of evidence demonstrating the heritabil- 
ity of many forms of nervous diseases which 
most commonly behave as recessives. Rosanoff 
and Orr," in a study of 206 matings between 
individuals from more or less insane stock, 
found 1,097 children, 146 of whom died in 
childhood. ‘There were 351 afflicted offspring 
to 586 normal. The theoretical expectations, 
knowing with more or less certainty the char- 
acter of the parents, was 359 to 578. There 
are presented (Figs. 12, 13, p. 135) two typical 
family pedigrees. In the first an insane man 
was twice married, each time to an eccentric 
woman, undoubtedly mildly insane. All the 
offspring were unbalanced. In the second case, 


‘Eugenics Record Office (Cold Spring Harbor, N.Y.), 
Bulletin, No. 5, ro1I. 


INHERITANCE OF HUMAN CHARACTERS 135 


those distinctly neurotic are indicated in solid 


color; those having a neurotic element in the 


0 ON ANLW ND FH 


a a 
{ 2. T3 


. Ignorant, “‘queer.”’ 

. Insane, was in sanitarium, committed suicide. 

i Eccentric, violent temper, ideas of persecution against neighbors. 
. Eccentric, not well-balanced. 

. Alcoholic, lazy, indolent. 

. Dementia preecox, paranoid, in state hospital. 

. Violent temper, queer, extreme dolichocephaly. 

. Defective, cranial malformation. 

. Inferior, ‘‘slow.” 


Fic. 12.—From Rosanoff and Orr, Inheritance of Insanity 





. Epileptic. 

. Insane for a time, recovered. 

Epileptic imbecile. 

. Imbecile. 

Melancholy in early married life, recovered. 
Insane five years, was in state hospital, recovered. 
Insomnia, neuralgia. 

; Daughter had spells of excitement. 

. Feeble-minded. 

Dementia precox, katatonic, in state penta 
. Died of marasmus, had one convulsion. 


HOO CON ONBRWN HH 


HH 


Fic. 13.—From Rosanoff and Orr, Inheritance of Insanity 


germ material are shaded. It might seem as if 


insane individuals would scarcely add mate- 


rially to the general population, since they are 


136 THE THIRD AND FouRTH GENERATION 


commonly in asylums. Often, however, the 
inherited insanity does not manifest itself until 
past middle life, when they have already 
married and started a family. Moreover, 
those hybrid individuals in whom the insane 
tendency is present alongside of the normal 
determiner appear as normal individuals. Fre- 
quently they can be detected only by an 
examination of the pedigree. If such individ- 
uals mate, one-fourth of the offspring would be 
expected to be insane. 

Early modern European history centers 
about the doings of a few great men and 
women. Peter the Great of Russia, Ferdinand 
and Isabella and Charles V of Spain, Frederick 
the Great of Prussia, Gustavus Adolphus 
and Charles XII of Sweden, are among the 
most brilliant of these potent individuals that 
shaped the destinies of Europe during this 
period. It is interesting to note how their 
characters are determined (and through them 
national destinies are apparently decided in 
no small measure) by the hereditary concentra- 
tion of ability due to lucky royal matings, 


137 


INHERITANCE OF HUMAN CHARACTERS 








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138 THE THIRD AND FOURTH GENERATION 


and how their genius is dissipated by unwise 
matings. 

Peter the Great of Russia came as a brilliant 
type from a good stock, though with a very 
evident taint of epilepsy and feeble-mindedness. 
He himself was an epileptic. His father, 
grandfather, and great-grandfather had been 
men of large ability. They had married 
peasant girls, as was the custom of the czars. 
Peter’s own brothers and sisters were in no way 
remarkable. His half-sister Sophia was a 
woman of marked ability, although two of her 
brothers were imbeciles, one also an epileptic. 
As will be seen from the pedigree, the epilepsy, 
imbecility, and mediocrity appear in both 
Peter’s children and grandchildren, as well as 
in those of his imbecile half-brother, Ivan. It 
is interesting to note from the pedigree that the 
feeble-mindedness and epilepsy seem to cling 
to the males quite persistently. The females 
of the family are much more apt to be brilliant 
and virtuous. Peter the Great’s own son Alexis 
was a poor dissolute specimen, and although he 
married Charlotte, the angelic daughter of a 


INHERITANCE OF HUMAN CHARACTERS 139 


great line, the house of Brunswick, the son of 
this mating was Peter II, of unstable mind, 
while the daughter Natalia was as sweet as she 
was energetic. 

Isabella and Ferdinand were both de- 
scendants from lines of very great individuals, 
although in each case there is insanity in the 
family. Isabella herself comes from an insane 
mother and an imbecile father, but her grand- 
parents and great-grandparents were well- 
balanced and able. The data for the charts of 
these royal families were taken largely from 
F. A. Wood’s Mental and Moral Heredity in 
Royalty, supplemented with information from 
other sources. He grades the individuals on a 
scale of ro. Ten represents very high ability, 
as determined by the comparative amount of 
space and laudation given to the individual in 
such standard works as Lippincott’s Biograpi- 
cal Dictionary. Five out of eight of Isabella’s 
great-grandparents rank very high. John the 
Great of Portugal, twice her great-grandfather, 
has a grade of 10. John of Gault, twice her 
great-grandfather, has a grade of 8, as does also 


140 ‘THE THIRD AND FOURTH GENERATION 


John of Castile, while Henry III of Castile, one 
of her grandparents, is designated the model 
king. Ferdinand I of Aragon, the grandfather 
of Ferdinand, is a brother of this same Henry 
III of Castile, and is also an exceedingly able 
king. Of the children of Ferdinand and Isabella, 
most were mediocre or distinctly inferior. 
Joanna was insane. In the next generation, 
however, appears Charles V, whose reign marked 
the acme of Spain’s greatness, partially due to 
his own ability, partially due to the momentum 
of those movements that were instituted by his 
illustrious grandparents. Charles V married 
his own cousin, as did also John IIT. Children 
of these two matings married, and Don Carlos, 
child of this latter marriage, was madly 
depraved and cruel. 

When insanity and brilliancy are found in 
the ancestry, it seems merely a matter of chance 
as to whether the determiners for greatness will 
be thrown together in the union of sperm and 
egg or those for insanity. We can predict with 
some certainty that, in a large number of 
offspring, ability will reappear and insanity will 


I4I 


INHERITANCE OF HUMAN CHARACTERS 


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142 THE THIRD AND FOURTH GENERATION 


reappear, but just what individual each will 
strike it is impossible to prophesy without 
knowing much more definitely the nature of the 
germ plasm involved. One may say that the 
convergence of a number of lines of descent 
from great ancestors toward one individual 
makes it probable that he will be exceptionally 
able. 

This is nowhere better illustrated than in 
the family tree of Frederick the Great of the 
Prussian house of Hohenzollern, as will be seen 
from the chart on page 143. Of his great- 
grandparents, three scale ro, one 9, one 8, two 7, 
and one 6. Not one is below mediocrity, and 
the majority are of very high grade. Of his 
fourteen ancestors back three generations, only 
one is distinctly inferior. Of his brothers and 
sisters, four are distinctly great, three mediocre, 
and one inferior. 

It is interesting to trace the effect of the 
mating of such splendid stock with another 
brillant line, that of the Swedish royal house. 
Gustavus I, or Gustavus Vasa, is another 
instance of the brilliant mutant, with some 


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144 THE THIRD AND FOURTH GENERATION 


taint of neurosis. He married a gentle and 
tactful princess; their son Charles [IX was a 
very able man, although of their three other 
children one was insane and two weak. The 
children of Charles [IX were both remarkably 
able. The daughter Catherine becomes the 
mother of a later succession of kings. Her son 
Charles X and his son Charles XI were rather 
mediocre; but Charles XI, with this fine 
stock behind him, married Ulrica Eleanor (7), 
granddaughter of Christian IV of Denmark, the 
most brilliant of all Danish sovereigns, and 
Charles XII, their son, is pronounced by 
Voltaire the most remarkable man who ever 
existed. Charles XII had no children: the 
succession passed to his sister’s son, Adolph 
Frederick of Holstein-Gotthorp, who married 
Louisa Ulrica, sister of Frederick the Great of 
Prussia. The result of this union of two great 
lines of hereditary ability was Gustavus III, a 
fit successor of Gustavus Vasa, Gustavus 
Adolphus, and Charles XII; he was ‘‘a prodigy 
of talents,” statesman, poet, dramatist. 


145 


INHERITANCE OF HUMAN CHARACTERS 


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146 THE THIRD AND FOURTH GENERATION 


QUESTIONS 


1. Can you give any example of the inheritance 
of a physical human character not cited in the text ? 

2. How would you state the evidence on the 
probability of the inheritance of mental peculiarities ? 

3. Does it seem to you likely that the course of 
history has been affected by the phenomena of hered- 
ity? What evidence would you present for your view ? 

4. Read the delightful story of the betrothal of 
Isaac and Rebekah (Gen., chap. 24), and note how the 
idea of keeping the strain pure dominates the narrative. 
This of course reveals what man had learned by 
practical experience. 

5. Has heredity been powerful in shaping up the 
destinies of your own particular historical hero ? 

6. How may the genius be accounted for other 
than as a result of descent from a line of great an- 
cestors ? 


CHAPTER X 


THE PRACTICAL PROBLEM OF HUMAN 
HEREDITY 

Primitive man sees his world ruled by 
capricious gods, whose whims and fancies can 
seldom be accurately anticipated, whose wrath 
must be appeased, whose favor must be won. 
Life is a bagatelle, a game of chance, since 
so many incalculable personalities, gods and 
demons, fairies and goblins, unexpectedly enter 
as determining | factors. Science has largely 
relieved man of this dread uncertainty and 
replaced chance by law and order. Yet we are 
slow to apprehend this revelation. Instead of 
inquiring beforehand as to what factors are 
involved in an undertaking, and as to what the 
resultant of their orderly interplay is bound to 
be, we act on sudden impulse, react to uncon- 
trolled desire, and then vainly hope that 
things will in some way chance to come out 
right. 


147 — 


148 THE THIRD AND FOURTH GENERATION 


This has been notably true in sex relations 
and in matters of heredity. Possibly, when 
little or nothing was known of the laws that 
govern hereditary phenomena, some trust in 
luck was excusable, and when knowledge of 
matters pertaining to sex was tabooed and only 
clandestinely acquired, about the only recourse 
was blind dependence on chance. 

If, then, the preceding chapters have accom- 
plished their purpose, they have left the 
impression that the young people, who are to be 
the mothers and fathers of the next generation, 
have a right to a frank, yet reverent, presenta- 
tion of reproduction and heredity, at least a 
presentation sufficient to make them realize 
that these phenomena are well within the pale 
of law and order. Now, one may not marry 
into a family with a persistent tubercular 
history in the blind hope that luck will prevent 
the reappearance of the defective tendency in 
future generations; we know what to expect. 
We know that insane and feeble-minded stock 
is prone to reproduce insanity and_ feeble- 
mindedness, and that, on the other hand, 


PROBLEM OF HUMAN HEREDITY 149 


ability mated with ability tends to repro- 
duce ability. The expert dairyman carefully 
inquires into the purity of strain and ancestral 
performance of the animal he mates with his 
choice cows. The farmer insists on a hog with 
certified ancestors. We have sense enough to 
apply such knowledge of heredity as we possess 
to our farm stock. It seems little enough to ask 
that we should exercise as much good sense in 
producing children as we do in the production 
of hogs and corn. ‘That does not mean that we 
can apply the method of the cattle pen to 
human relations, but merely that we adopt 
caution and intelligent foresight in founding a 
family commensurate with that used by the wise 
breeder of plant or animal stock. 

Briefly, the knowledge now at our command 
for this purpose may be summarized as follows. 
Whenever plants or animals differing from each 
other in one or more particulars are interbred, 
the transmission of those factors, whose inter- 
play determines the hereditary characters, is in 
accordance (generation after generation) with 
the simple Mendelian laws. Even those cases 


150 THE THIRD AND FOURTH GENERATION 


that are apparent exceptions, like eye color in 
the fruit fly and color blindness in men, are 
found to be explicable as Mendelian phenomena 
when they are considered as sex-linked charac- 
ters. So far as our accurate data go, they 
indicate that the inheritance of human physical 
characters is truly Mendelian, so that, knowing 
the hair color, eye color, height, etc., of the 
parents, one can predict with accuracy the 
probable characters of the children. Disease 
tendencies (but not the diseases themselves) 
usually behave as Mendelian recessives. Cer- 
tain diseases primarily affecting the sex organs, 
syphilis and gonorrhea, while not heritable, are 
communicated from mother to child at time of 
birth, and from person to person, largely, but 
not wholly, by impure sexual relations. ‘These 
diseases are exceedingly virulent, cause untold 
misery, are more prevalent and more terrible 
than tuberculosis, and, while curable in a 
minority of the cases, are often uncured, and 
hence a source of contagion to innocent persons, 
especially to wives and children who come in 
contact with a diseased man. 


PROBLEM OF HUMAN HEREDITY 151 


The facts seem to indicate that abnormal 
conditions of the nervous system, resulting in 
alcoholic mania, epilepsy, feeble-mindedness, 
and insanity, are also heritable, and probably in 
Mendelian fashion; at least the evidence is sufh- 
cient to induce the cautious individual to base 
action on such a hypothesis. Similarly, the evi- 
dence seems to show that mental ability also is 
heritable, though so many facts are involved in 
such a complicated thing as ‘‘ability”’ that we 
may make this assertion in a tentative way only. 

With these facts in mind, what policies may 
be adopted to guide action that aims at an 
improvement of a family, a race, or a people ? 
We must bear in mind that improving the 
environment may enlarge opportunity. Train- 
ing may develop individual capacity to the limit, 
but that limit is set by the hereditary equip- 
ment. The hope of racial improvement is in 
selective breeding, and this hope must be 
realized by (1) stimulating reproduction in the 
best stock, (2) checking it in the poorest. The 
same method has been effective in man’s 
improvement of domestic plants and animals. 


152 THE THIRD AND FoURTH GENERATION 


It is one of nature’s potent methods for the 
improvement of all living things, the elimina- 
tion of the unfit, the reproduction of the fit. 

Any farmer would promptly predict the 
fate of a herd of cattle in which the scrub stock 
was allowed to breed faster than the pedigreed 
stock. Yet there is no doubt that in civilized 
countries large families are the rule among the 
undesirable elements and the exception in the 
best stock. Pierson carefully prepared a tabu- 
lation showing the relative fertility of various 
stocks. ‘The mentally defective, criminal, deaf, 
mute, and degenerate stocks head the list with 
average families of from five to seven children, 
while the families of the college-bred pro- 
fessional men average less than two. Cattell 
gathered data for 917 American men conspicu- 
ous in scientific achievement and found they 
averaged 2.22 children per family, while the 
average number of children in the families of 
the parents of these men was 4.66, a decline in 
the birth-rate in this evidently superior stock 
of more than one-half in one generation." 


t Scientific Monthly, IV (1917), 252. 


PROBLEM OF HUMAN HEREDITY 153 


Probably the most potent remedy for this 
situation is the development of a sense of 
obligation on the part of the really able parents 
to increase the size of their families as a means 
of contributing to social improvement, rather 
than voluntarily restricting the size in the 
interests of ease and luxury, as seems to be 
now so prevalent a custom. 

Social and economic readjustments, which 
make possible earlier marriages in the desirable 
classes, are important factors in any eugenic 
program, for any social group that marries 
at twenty will in a few generations outnumber 
and replace a competing class that marries at 
thirty. An economy of a few years in the 
process of education, a larger wage to the 
young, skilled worker, or a reduction in the cost 
of the necessities of life by governmental 
control of the sources of supply, by inventions 
that cheapen production, by better methods in 
agriculture—such apparently unrelated factors 
are really determining influences in the size of 
families, and so contribute directly to racial 
improvement by selective breeding. 


154 THE THIRD AND FouRTH GENERATION 


It is easy to devise methods for checking the 
increase of the undesirable elements of the 
population, but not at all easy to enforce these 
means of control. Segregation under conditions 
which preclude child-bearing, even sterilization, 
are devices in actual practice in several states, 
but as yet public sentiment is not sufficiently 
aroused to make their enforcement very effec- 
tive. Consequently such groups as_ the 
epileptic, feeble-minded, and insane are still 
multiplying more rapidly than is even the 
general run of the population, and much more 
rapidly than the very select strains. In ancient 
Athens such defectives were eliminated by the 
state as a serious menace. Our civilization, 
more considerate of individual right and less 
impressed with the welfare of the state, not 
only lets them live, but hesitates to protect 
itself from their undue increase. 

A certain degree of family pride is a valu- 
able eugenic asset, not the snobbish sort that 
ostentatiously flounts cheap titles or chance 
wealth in the faces of its neighbors, but a 


respect for the family traditions, generation 


PROBLEM OF HUMAN HEREDITY 155 


after generation, of the really fine achievements. 
The individual who feels that he h:s behind him 
a line of immediate ancestors who have accom- 
plished things, men and women who have left 
a heroic impress on their community, even 
if it were not a large one, will be inspired to do 
a man’s part in the world. 

Finally, it is to be admitted that the eugenist 
is an idealist, looking forward hopefully toward 
the things that are to be. How soon they will 
be accomplished will depend somewhat on how 
readily Cupid can be induced to submit to 
established law, somewhat on social readjust- 
ments, and somewhat on the good sense of 
another generation. This generation sees the 
vision, and has faith that the next will trans- 
mute much of it into accomplishment, for 

So nigh is grandeur to our dust, 
So near is God to man, 


When Duty whispers low, ‘‘Thou must!” 
The youth replies, “I can.” 


APPENDIX 


BOOKS FOR REFERENCE OR FURTHER 
READING 


Bateson, W. Mendel’s Principles of Heredity. Cambridge 
University Press, 1909. Contains translation of 


Mendel’s original papers. 





Problems in Genetics. Yale University Press, 1913. 

Castle, Coulter, Davenport, East, and Tower. Heredity 
and Eugenics. The University of Chicago Press, 1912. 

Castle, W. E. Heredity in Relation to Evolution and Animal 
Breeding. D. Appleton & Co., 1912. 

Castle, W. E., and Phillips, J.C. On Germinal Transplanta- 
tion in Vertebrates. Carnegie Institution, Washington, 
Publication Number 144, Io1t. 

Coulter, John M. Fundamentals of Plant Breeding. D. 
Appleton & Co., 1914. 

Davenport, C. B. Heredity in Relation to Evugenics. 
Henry Holt & Co., rortr. 

Heredity of Skin Color in Negro-White Crosses. 

Carnegie Institution, Washington, Publication Number 





188, 1914. 

Dugdale, R. L. The Jukes; A Study in Crime, Pauperism, 
Disease and Heredity. G. P. Putnam’s Sons, 1877. 
Estabrook, Arthur H. The Jukes in 1915. Carnegie 
Institution, Washington, Publication Number 240, 

1916. 
156 


APPENDIX T57 


Galton, Francis. Hereditary Genius: An Inquiry into Its 
Laws and Consequences. The Macmillan Co., 1860. 

Natural Inheritance. The Macmillan Co., 1889. 

———. English Men of Science; Their Nature and Nurture. 
D. Appleton & Co., 1895. 

Galton, Francis, and Schuster, Edgar. Noteworthy Families. 





J. Murray, 1906. 
Goddard, Henry H. Feeblemindedness; Its Causes and 
Consequences. The Macmillan Co., 1914. 
The Kallikak Family, A Study in the Heredity 
of Feeblemindedness. The Macmillan Co., 1912. 





Morgan, Thomas H. Heredity and Sex. Columbia Uni- 
versity Press, 1913. 

A Critique of the Theory of Evolution. Princeton 

University Press, 1916. 





Pearson, Karl. Tuberculosis, Heredity and Environment. 
Cambridge University Press, to12. 

; Saleeby, Caleb W. Parenthood and Race Culture; An 
Outline of Eugenics. Cassell & Co., 1909. 

Stockard, Chas. R. “The Effect of Intoxicating the Male 
Parent,” American Naturalist, XLVII, November, 1913. 

Tower, W.L. An Investigation of Evolution in Chrysomelid 
Beetles of the Genus Leptinotarsa. Carnegie Institution, 
Washington, Publication Number 48, 1906. 

Wilson, E. B. The Cell in Development and Inheritance. 
Columbia University Press, 1900. 

Woods, Frederick A. Mental and Moral Heredity in 
Royalty. Henry Holt & Co., 1906. 


Cy it 





INDEX 


BN | 


i] * 


tee Pig 





INDEX 


Ability, inheritance of: animal, 8; 
human, 10, 149, I51 


Ability, negro, 96 


Acquired character. See Ac- 
quired Modification 

Acquired modification: defined, 
ror; not inherited, 106; evi- 


dence of Alpine flowers, 102; 
chipmunk, 104; Chinese women, 
105; corn, 102; Flathead In- 
dians, 105 

Adaptation, 103, 104 


Alcohol: effects inherited, 115, 
116, 117; effects on guinea-pigs, 
114; effects on white rats, 116; 
influences germ cells directly, 
116 


Alcoholism, 151; a symptom, 117 

Alix, pedigree of, 6 

Alpine environment, 102 

American men of science, families 
of, 152 

Ancestry, pride in, 8, 154 

Ancon sheep, 50 

Andalusian fowls, 44 

Anther, 20 


Ascaris, early separation of soma 
and germ plasm, 109 


Athens, disposition of undesir- 
ables in, 154 


Bach, Johann Sebastian, family 
connections, 12 


Bateson, experiments with sweet 
peas, 86 


Beans, pure-line, 58 

Birth, contagion at, 118 
Birthmarks, 82 

Birth-rate decreasing, 152 
Birth registration, 122 
Blindness, inheritance of, 119 


161 


Blueberry under domestication, 48 


Boveri, experiments with denucle- 
ated eggs, 72 


Brachydactylism, inheritance of, 
124 
Breeder, methods of, 64 


Breeding: mass, 57, 65; pure- 
line, 58, 65; selective, 153 


Burbank, Luther, production of 
new types, 53, 65; plumcot, 65; 
potato, 54; seedless prune, 
65; royal walnut, 65; Shasta 
daisy, 53 


Cabbage, disease-resisting, 51 

Cataract, inheritance of, 124 

Cattle, 48, 50, 82 

Cell, 22, 23, 67, 73; division, 60, 
41 

Characters, acquired defined, tor 
See Acquired Modifications 


Characters, new in evolution, ror 

Charles XII, the Great, of 
Sweden, 144, 145 

Chickens, 43, 44, 48, 64; Andalu- 
sian, 44; breeding for increased 
egg production, 64 


Chinese women, feet of, 105 
Chipmunk, species developed in 
isolation, 104 


Chromatin, 69, 70 


Chromosomes, 70, 73; diploid 
number, 75; equation division 
of, 74; haploid number, 75; 
individuality of, 75, 77; in 
equatorial plate, 74; maternal 
and paternal, 76; number of, 
73; number of, in white female, 
‘79; number of, in white male, 
79, 83; odd chromosome, 78; 
seat of factors, 81; sex chromo- 
some, 79, 98; x-chromosome, 78 


162 


Cleavage, 26 

Coat color in rabbits, 89 

Color blindness, 98 

Corn, 60, 61; early ripening, 102 
Cretinism, 133 


Crime, relation of, 
mindedness, 119 


Cross-pollination, 32 
Cuttings, propagation by, 84 


to feeble- 


Daisy, Shasta, 54 


Darbishire’s cross of yellow-green 
peas, 36 


Darley Arabian, 7 
Darwin, Charles, 10 
Darwin, Erasmus, 10 


Darwin-Wedgewood-Galton fam- 
ily, Io 


Deaf-mutism, 126 
Deafness, inheritance of, 126 
Determiners, 38, 39, 73, 78, 81 


de Vries, new species of evening 
primrose, 52 


Diploid number of chromosomes, 
75 

Disease, inheritance of, 111, I19 

Disease-resistant races, 52, 65 


Division of cell; equation, 74; 
reduction, 74, 79 


Dog, ancestry of, 47 

Domestic animals, origin of, 47 
Domestication, 48 

Dominance, 44 

Dominant, 36, 43, 44 


“ducability of white rats, affected 
by alcohol, 116 


Education, effects not heritable, 
112 

Edwards family, 13 

Edwards, Jonathan, 13, 14 

Edwards, Richard, 15 


Egg, 21, 22, 24, 25, 67, 72. See 
Fertilization and Cleavage 


THE THIRD AND FOURTH GENERATION 


Embryo, 23, 24 

Environment: effect of, 17, 102, 
103, 104; direct effect on germ 
plasm, 113. See also Acquired 
Modification; Isolation 


Environment vs. heredity, 17 
Epilepsy, inheritance of, 151 
Equatorial plate, 70, 74 
Eugenic laboratories, 123 
Eugenics, vili, 157 
Evolution, doctrine of, tot 


Factorial hypothesis, 88 
Factors, 86, 88, 89 


Families: large, 152; of American 
men of science, 152; of unde- 
sirable classes, 152 


Feeble-minded, number of, 132; 
segregation of, 134; steriliza- 
tion of, 120 

Feeble-mindedness, inheritance of, 
LIG/ 122,125, 132 

Ferdinand of Spain, 139, 141 

Flathead Indian, head of, 105 

Four-o’-clocks, 44 

Frederick the Great, 142, 143 


Frogs’ eggs, deposit and develop- 
ment of, 25 


Fruit fly, 81, 97 


Galton family pedigree, to 

Galton laboratory, 123 

Galton, Sir Francis, 11; 
of ability, ro 

Galton’s law, 58 

Genius, 140 

Genotype, oI 

Geographical isolation, 104 


Germ plasm, 117; continuity of, 
107; directly affected by envi- 
ronment, 113; early separation 
of soma from, 109; unaffected 
by soma, I10 


Godolphin, Arabian, 7 
Gonorrhea, 118, 150 


studies 


INDEX 


Grape, Concord, 49 


Guinea-pigs: Brown-Sequard ex- 
periments with, 106; Mendelian 
inheritance of coat color, 42; 
Stockard’s experiments with 
alcoholized, 114; transplanted 
ovaries in, 110 


Haploid number of chromosomes, 
v Oey, 79 

Hapsburg jaw, 30 

Harelip, 87 

Heredity. See Inheritance 

Hereford cattle, 50 

Hohenzollerns, pedigree of, 142, 
143 

Honey production, 8 

Horse, champion trotting, 5 

Hybrid, 34, 43, 44, 62 

Hybridization, 46, 57, 60 


Identical twins, 83 

Immigrants, inspection for de- 
fectives, 131 

Inbreeding, 116, 117 

Inheritance: laws of, 30, 31; of 
DINGY eye LO A0, L5ts) OL 
acquired modifications, 1o1—6; 
of alcoholism, 115; of blind- 
ness, 126; of cataract, 124; of 
disease, 111, 119; of epilepsy, 
151; of feeble-mindedness, tro, 
123, 128, 132; of human char- 
acters, 122; of insanity, 134, 
140; of tuberculosis, 111; 
social, 112, 113 

Insanity, inheritance of, 119, 123, 
134, I51 

Isaac and Rebekah, 146 

Isabella, queen of Spain, 139, 141 


Isolation, geographical, 104 


Jacob and the spotted cattle, 82 
Johannson’s pure-line beans, 58 
Judges, English, 11 

Jukes, 13 


163 


Kallikak, Martin, 132 
King Melia Rioter, 8, 9, 14 


Law, Mendel’s, 30, 31 
Learning in white rats, 116 


Mandrake or May apple blossom, 
parts of, 19, 24 


Marriage, age of, 153 
Max-Jukes and progeny, 13, 15 
Melia Rioter, 14, pedigree of, 9 
Mendel, Gregor, 31 

Mendelian ratios, 41, 42 
Mendel’s law, 32, 149 
Messenger, 6, 7 

Milk production, 8 

Mitosis or cell division, 69-71 


Modifications, acquired. See Ac- 
quired Modifications 


Mulatto, 94 
Mutation, 53 


Navel orange, 50 
Negro, 94, 96 


Nilsson-Ehle and work of Swedish 
experiment station, 93 


Orange, navel, 50 
Ovaries of guinea-pig 
planted, 110 


Ovary, 21 
Ovules, 21 
Ovum oregg. See Egg 


trans- 


Pacers from Messenger stock, 8 


Peas, 31, 86, 87; sweet, Bateson’s 
experiments with, 86 


Pedigree: of Alix, 6; of Bach 
family, 12; of Charles XII, 
144; of Darwin family, 10; of 
Ferdinand and Isabella, 139; of 
Hohenzollerns, 142; of Melia 
Rioter 14, 9; of Peter the 
Great, 137 


Peter the Great, 137 


. 


164 


Phenotype, o1 

Pigeons, origin of domestic, 48 
Pistil, 19 

Pollen, 22 

Polydactylism, 124 
Potato-beetle, 113 

Potato, Burbank’s, 54 


Poultry, selection for egg pro- 
duction, 64 


Prenatal influence, 81 

Prepotency, 64 

Primrose, evening and mutants, 
52 

Protoplasm, 67 

Pure line in breeding, 58, 59 


Rabbits, factors in coat cojor, 89 

Racial improvement, 151 

Rebekah and Isaac, 146 

Recessive, 36, 42 

Reduction of chromosomes, 74, 84 

Reproduction, 28; value of sexual, 
83 

Reversion, 87 

Romanhoffs, family pedigree, 137 


Saltation, 53 

Seed, 24 

Segregation of characters, 40, 78 

Sex chromosome, 78, 79 

Sex determination in-man, 79 

Sex-determiner, 79 

Sexes, equality in numbers, 80 

Sex-linked characters, 97, 98, 150 

Sex-linked inheritance, 97 

Sexual impurity, diseases of, 119, 
150 

Sexual reproduction, value of, 83 

Sheep, Ancons, 49 

Sins of the fathers, 120, 121 


THE THIRD AND FOURTH GENERATION 


Social inheritance, 112, I13 
Somatoplasm, 107, IIo 
Sperm, 25, 28, 67, 72 
““Sports,’’ 52, 64 

Stamens, 19 


Sterilization of the undesirables, 
120 


Syphilis, 118, 150 


Tadpole, 27 

“*Tail-male’”’ descent, 7 

Trotted mile, time of, 4 
Trotters, American, 5 
Tuberculosis, inheritance of, 111 
Turkey under domestication, 48 
Tuttle, Mary, 15 

Twins, identical, 83 

Types, improved, 59 


Uhlan, champion trotter, 5 

Undesirables, propagation of, 152, 
154 

Unit character, 88 

Uterus, 66 


Variation, 83 


Venereal diseases, 118, 119, 120, 
150 
de Vries, Hugo, 53 


Wedgewood, Josiah, 10 


Weismann, theory of continuity 
of germ plasm, 107 


Wheat, 56, 58, 93 


White rats, experiments with 
alcoholized, 116 
Womb, 66 


X-chromosome or sex chromo- 
some, 78 


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